This is an automated email from the ASF dual-hosted git repository.
spmallette pushed a commit to branch TINKERPOP-2681
in repository https://gitbox.apache.org/repos/asf/tinkerpop.git
commit 8939d5ea4a1ad7dcf27c5b9c807ae17fa93078ad
Author: Stephen Mallette <stepm...@amazon.com>
AuthorDate: Mon Feb 7 07:27:45 2022 -0500
TINKERPOP-2681 Finalize mergeV semantics around null/empty args
---
docs/src/dev/provider/gremlin-semantics.asciidoc | 66 ++++++++++++
.../language/grammar/TraversalMethodVisitor.java | 10 ++
.../grammar/TraversalSourceSpawnMethodVisitor.java | 6 ++
.../traversal/step/map/MergeVertexStep.java | 90 ++++++++++------
gremlin-language/src/main/antlr4/Gremlin.g4 | 11 +-
gremlin-test/features/map/MergeVertex.feature | 116 +++++++++++++++++++++
.../traversal/step/map/TinkerMergeVertexStep.java | 4 +-
7 files changed, 263 insertions(+), 40 deletions(-)
diff --git a/docs/src/dev/provider/gremlin-semantics.asciidoc
b/docs/src/dev/provider/gremlin-semantics.asciidoc
index 3bb1244..c6a0223 100644
--- a/docs/src/dev/provider/gremlin-semantics.asciidoc
+++ b/docs/src/dev/provider/gremlin-semantics.asciidoc
@@ -590,3 +590,69 @@ Same as Comparability, except orderability semantics apply
for element compariso
* If the unknown arguments are of different types or do not define a natural
order, order first by Classname, then
by `Object.toString()`.
+== Steps
+
+While TinkerPop has a full test suite for validating functionality of Gremlin,
tests alone aren't always exhaustive or
+fully demonstrative of Gremlin step semantics. It is also hard to simply read
the tests to understand exactly how a
+step is meant to behave. This section discusses the semantics for individual
steps to help users and providers
+understand implementation expectations.
+
+=== mergeE()
+
+
+
+=== mergeV()
+
+*Description:* Provides upsert-like functionality for vertices.
+*Syntax:* `mergeV()` | `mergeV(Map)` | `mergeV(Traversal)`
+
+[width="100%",options="header"]
+|=========================================================
+|Start Step |Mid Step |Modulated |Domain |Range
+|Y |Y |`option()` |`Map` |`Vertex`
+
+*Arguments:*
+
+* `searchCreate` - A `Map` used to match a `Vertex` and if not found be the
default set of data to create the new one.
+* `onCreate` - A `Map` that is the override to the default of `searchCreate`
+* `onMatch` - A `Map` used to update the `Vertex` that is found using the
`searchCreate` criteria.
+
+The `searchCreate` and `onCreate` `Map` instances must consists of any
combination of `T.id`, `T.label`, or arbitrary
+`String` keys (which are assumed to be vertex properties). The `onMatch` `Map`
instance only allows for `String` keys
+as the `id` and `label` of a `Vertex` are immutable. Values for these valid
keys that are `null` will be treated
+according to the semantics of the `addV()` step.
+
+The `Map` that is used as the argument for `searchCreate` may be assigned from
the incoming `Traverser` for the no-arg
+`mergeV()`. If `mergeV(Map)` is used, then it will override the incoming
`Traverser`. If `mergeV(Traversal)` is used,
+the `Traversal` argument must resolve to a `Map` and it would also override
the incoming Traverser. The `onCreate` and
+`onMatch` arguments are assigned via modulation as described below.
+
+[width="100%",options="header"]
+|=========================================================
+|Event |Null `Map` |Empty `Map`
+|Search |Filters all vertices |Matches all vertices
+|Create |No new vertex |New vertex with defaults
+|Update |No update to matched vertex |No update to matched vertex
+|=========================================================
+
+If `T.id` is used for `searchCreate` or `onCreate`, it may be ignored for
vertex creation if the `Graph` does not
+support user supplied identifiers.
+
+*Modulation:*
+
+* `option(Merge, Map)` - Sets the `onCreate` or `onMatch` arguments directly.
+* `option(Merge, Traversal)` - Sets the `onCreate` or `onMatch` arguments
dynamically where the `Traversal` must
+resolve to a `Map`.
+
+*Exceptions*
+
+* `Map` arguments are validated for their keys resulting in exception if they
do not meet requirements defined above.
+* Use of `T.label` should always have a value that is a `String`.
+
+*Considerations:*
+
+* `mergeV()` Can only be used mid-traversal. It is not a start step.
+* As is common to Gremlin, it is expected that `Traversal` arguments may
utilize `sideEffect()` steps.
+
+See:
link:https://github.com/apache/tinkerpop/tree/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeVertexStep.java[source],
+link:https://tinkerpop.apache.org/docs/current/reference/#mergev-step[reference]
\ No newline at end of file
diff --git
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalMethodVisitor.java
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalMethodVisitor.java
index ed1ae19..ed630cc 100644
---
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalMethodVisitor.java
+++
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalMethodVisitor.java
@@ -94,6 +94,9 @@ public class TraversalMethodVisitor extends
TraversalRootVisitor<GraphTraversal>
*/
@Override
public GraphTraversal visitTraversalMethod_mergeV_Map(final
GremlinParser.TraversalMethod_mergeV_MapContext ctx) {
+ if (ctx.nullLiteral() != null) {
+ return this.graphTraversal.mergeV((Map) null);
+ }
return
this.graphTraversal.mergeV(GenericLiteralVisitor.getMapLiteral(ctx.genericLiteralMap()));
}
@@ -126,6 +129,9 @@ public class TraversalMethodVisitor extends
TraversalRootVisitor<GraphTraversal>
*/
@Override
public GraphTraversal visitTraversalMethod_mergeE_Map(final
GremlinParser.TraversalMethod_mergeE_MapContext ctx) {
+ if (ctx.nullLiteral() != null) {
+ return this.graphTraversal.mergeE((Map) null);
+ }
return
this.graphTraversal.mergeE(GenericLiteralVisitor.getMapLiteral(ctx.genericLiteralMap()));
}
@@ -1035,6 +1041,10 @@ public class TraversalMethodVisitor extends
TraversalRootVisitor<GraphTraversal>
*/
@Override
public GraphTraversal visitTraversalMethod_option_Merge_Map(final
GremlinParser.TraversalMethod_option_Merge_MapContext ctx) {
+ if (ctx.nullLiteral() != null) {
+ return
this.graphTraversal.option(TraversalEnumParser.parseTraversalEnumFromContext(Merge.class,
ctx.traversalMerge()), (Map) null);
+ }
+
return
graphTraversal.option(TraversalEnumParser.parseTraversalEnumFromContext(Merge.class,
ctx.traversalMerge()),
(Map) new
GenericLiteralVisitor(antlr).visitGenericLiteralMap(ctx.genericLiteralMap()));
}
diff --git
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalSourceSpawnMethodVisitor.java
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalSourceSpawnMethodVisitor.java
index f7d04f7..6fdda82 100644
---
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalSourceSpawnMethodVisitor.java
+++
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/TraversalSourceSpawnMethodVisitor.java
@@ -119,6 +119,9 @@ public class TraversalSourceSpawnMethodVisitor extends
GremlinBaseVisitor<GraphT
@Override
public GraphTraversal visitTraversalSourceSpawnMethod_mergeV_Map(final
GremlinParser.TraversalSourceSpawnMethod_mergeV_MapContext ctx) {
+ if (ctx.nullLiteral() != null) {
+ return this.traversalSource.mergeV((Map) null);
+ }
return
this.traversalSource.mergeV(GenericLiteralVisitor.getMapLiteral(ctx.genericLiteralMap()));
}
@@ -134,6 +137,9 @@ public class TraversalSourceSpawnMethodVisitor extends
GremlinBaseVisitor<GraphT
@Override
public GraphTraversal visitTraversalSourceSpawnMethod_mergeE_Map(final
GremlinParser.TraversalSourceSpawnMethod_mergeE_MapContext ctx) {
+ if (ctx.nullLiteral() != null) {
+ return this.traversalSource.mergeE((Map) null);
+ }
return
this.traversalSource.mergeE(GenericLiteralVisitor.getMapLiteral(ctx.genericLiteralMap()));
}
}
diff --git
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeVertexStep.java
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeVertexStep.java
index b67621b..e92c11d 100644
---
a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeVertexStep.java
+++
b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeVertexStep.java
@@ -45,6 +45,7 @@ import
org.apache.tinkerpop.gremlin.structure.util.StringFactory;
import org.apache.tinkerpop.gremlin.util.iterator.IteratorUtils;
import java.util.ArrayList;
+import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
@@ -180,7 +181,9 @@ public class MergeVertexStep<S> extends FlatMapStep<S,
Vertex> implements Mutati
Stream<Vertex> stream;
// prioritize lookup by id
- if (search.containsKey(T.id))
+ if (null == search) {
+ return Stream.empty();
+ } else if (search.containsKey(T.id))
stream = IteratorUtils.stream(graph.vertices(search.get(T.id)));
else
stream = IteratorUtils.stream(graph.vertices());
@@ -216,21 +219,23 @@ public class MergeVertexStep<S> extends FlatMapStep<S,
Vertex> implements Mutati
final Map<String, Object> onMatchMap =
TraversalUtil.apply(traverser, onMatchTraversal);
validateMapInput(onMatchMap, true);
- onMatchMap.forEach((key, value) -> {
- // trigger callbacks for eventing - in this case, it's a
VertexPropertyChangedEvent. if there's no
- // registry/callbacks then just set the property
- if (this.callbackRegistry != null &&
!callbackRegistry.getCallbacks().isEmpty()) {
- final EventStrategy eventStrategy =
getTraversal().getStrategies().getStrategy(EventStrategy.class).get();
- final Property<?> p = v.property(key);
- final Property<Object> oldValue = p.isPresent() ?
eventStrategy.detach(v.property(key)) : null;
- final Event.VertexPropertyChangedEvent vpce = new
Event.VertexPropertyChangedEvent(eventStrategy.detach(v), oldValue, value);
- this.callbackRegistry.getCallbacks().forEach(c ->
c.accept(vpce));
- }
-
- // try to detect proper cardinality for the key according to
the graph
- final Graph graph = this.getTraversal().getGraph().get();
- v.property(graph.features().vertex().getCardinality(key), key,
value);
- });
+ if (onMatchMap != null) {
+ onMatchMap.forEach((key, value) -> {
+ // trigger callbacks for eventing - in this case, it's a
VertexPropertyChangedEvent. if there's no
+ // registry/callbacks then just set the property
+ if (this.callbackRegistry != null &&
!callbackRegistry.getCallbacks().isEmpty()) {
+ final EventStrategy eventStrategy =
getTraversal().getStrategies().getStrategy(EventStrategy.class).get();
+ final Property<?> p = v.property(key);
+ final Property<Object> oldValue = p.isPresent() ?
eventStrategy.detach(v.property(key)) : null;
+ final Event.VertexPropertyChangedEvent vpce = new
Event.VertexPropertyChangedEvent(eventStrategy.detach(v), oldValue, value);
+ this.callbackRegistry.getCallbacks().forEach(c ->
c.accept(vpce));
+ }
+
+ // try to detect proper cardinality for the key according
to the graph
+ final Graph graph = this.getTraversal().getGraph().get();
+ v.property(graph.features().vertex().getCardinality(key),
key, value);
+ });
+ }
return v;
});
@@ -251,21 +256,26 @@ public class MergeVertexStep<S> extends FlatMapStep<S,
Vertex> implements Mutati
// searchCreate should have already been validated so only do it
if it is overridden
if (useOnCreate) validateMapInput(m, false);
+ // if onCreate is null then it's a do nothing
final List<Object> keyValues = new ArrayList<>();
- for (Map.Entry<Object, Object> entry : m.entrySet()) {
- keyValues.add(entry.getKey());
- keyValues.add(entry.getValue());
- }
- vertex =
this.getTraversal().getGraph().get().addVertex(keyValues.toArray(new
Object[keyValues.size()]));
+ if (m != null) {
+ for (Map.Entry<Object, Object> entry : m.entrySet()) {
+ keyValues.add(entry.getKey());
+ keyValues.add(entry.getValue());
+ }
+ vertex =
this.getTraversal().getGraph().get().addVertex(keyValues.toArray(new
Object[keyValues.size()]));
- // trigger callbacks for eventing - in this case, it's a
VertexAddedEvent
- if (this.callbackRegistry != null &&
!callbackRegistry.getCallbacks().isEmpty()) {
- final EventStrategy eventStrategy =
getTraversal().getStrategies().getStrategy(EventStrategy.class).get();
- final Event.VertexAddedEvent vae = new
Event.VertexAddedEvent(eventStrategy.detach(vertex));
- this.callbackRegistry.getCallbacks().forEach(c ->
c.accept(vae));
- }
+ // trigger callbacks for eventing - in this case, it's a
VertexAddedEvent
+ if (this.callbackRegistry != null &&
!callbackRegistry.getCallbacks().isEmpty()) {
+ final EventStrategy eventStrategy =
getTraversal().getStrategies().getStrategy(EventStrategy.class).get();
+ final Event.VertexAddedEvent vae = new
Event.VertexAddedEvent(eventStrategy.detach(vertex));
+ this.callbackRegistry.getCallbacks().forEach(c ->
c.accept(vae));
+ }
- return IteratorUtils.of(vertex);
+ return IteratorUtils.of(vertex);
+ } else {
+ return Collections.emptyIterator();
+ }
}
}
@@ -274,6 +284,7 @@ public class MergeVertexStep<S> extends FlatMapStep<S,
Vertex> implements Mutati
* to immutable parts of an {@link Edge} (id, label, incident vertices) so
those can be ignored in the validation.
*/
public static void validateMapInput(final Map<?,Object> m, final boolean
ignoreTokens) {
+ if (null == m) return;
if (ignoreTokens) {
m.entrySet().stream().filter(e -> {
final Object k = e.getKey();
@@ -295,11 +306,24 @@ public class MergeVertexStep<S> extends FlatMapStep<S,
Vertex> implements Mutati
}
if (!ignoreTokens) {
- m.entrySet().stream().filter(e -> e.getKey() == T.label &&
!(e.getValue() instanceof String)).findFirst().map(e -> {
- throw new IllegalArgumentException(String.format(
- "mergeV() expects T.label value to be of String -
found: %s",
- e.getValue().getClass().getSimpleName()));
- });
+ if (m.containsKey(T.id)) {
+ if (null == m.get(T.id)) {
+ throw new IllegalArgumentException("Vertex id cannot be
null");
+ }
+ }
+
+ if (m.containsKey(T.label)) {
+ final Object l = m.get(T.label);
+ if (null == l) {
+ throw new IllegalArgumentException("Vertex label cannot be
null");
+ }
+
+ if (!(l instanceof String)) {
+ throw new IllegalArgumentException(String.format(
+ "mergeV() expects T.label value to be of String -
found: %s",
+ l.getClass().getSimpleName()));
+ }
+ }
}
}
diff --git a/gremlin-language/src/main/antlr4/Gremlin.g4
b/gremlin-language/src/main/antlr4/Gremlin.g4
index f359dd8..298cc3e 100644
--- a/gremlin-language/src/main/antlr4/Gremlin.g4
+++ b/gremlin-language/src/main/antlr4/Gremlin.g4
@@ -131,12 +131,12 @@ traversalSourceSpawnMethod_io
;
traversalSourceSpawnMethod_mergeV
- : 'mergeV' LPAREN genericLiteralMap RPAREN
#traversalSourceSpawnMethod_mergeV_Map
+ : 'mergeV' LPAREN (genericLiteralMap | nullLiteral) RPAREN
#traversalSourceSpawnMethod_mergeV_Map
| 'mergeV' LPAREN nestedTraversal RPAREN
#traversalSourceSpawnMethod_mergeV_Traversal
;
traversalSourceSpawnMethod_mergeE
- : 'mergeE' LPAREN genericLiteralMap RPAREN
#traversalSourceSpawnMethod_mergeE_Map
+ : 'mergeE' LPAREN (genericLiteralMap | nullLiteral) RPAREN
#traversalSourceSpawnMethod_mergeE_Map
| 'mergeE' LPAREN nestedTraversal RPAREN
#traversalSourceSpawnMethod_mergeE_Traversal
;
@@ -288,17 +288,16 @@ traversalMethod_addV
traversalMethod_mergeV
: 'mergeV' LPAREN RPAREN #traversalMethod_mergeV_empty
- | 'mergeV' LPAREN genericLiteralMap RPAREN #traversalMethod_mergeV_Map
+ | 'mergeV' LPAREN (genericLiteralMap | nullLiteral) RPAREN
#traversalMethod_mergeV_Map
| 'mergeV' LPAREN nestedTraversal RPAREN #traversalMethod_mergeV_Traversal
;
traversalMethod_mergeE
: 'mergeE' LPAREN RPAREN #traversalMethod_mergeE_empty
- | 'mergeE' LPAREN genericLiteralMap RPAREN #traversalMethod_mergeE_Map
+ | 'mergeE' LPAREN (genericLiteralMap | nullLiteral) RPAREN
#traversalMethod_mergeE_Map
| 'mergeE' LPAREN nestedTraversal RPAREN #traversalMethod_mergeE_Traversal
;
-
traversalMethod_aggregate
: 'aggregate' LPAREN traversalScope COMMA stringLiteral RPAREN
#traversalMethod_aggregate_Scope_String
| 'aggregate' LPAREN stringLiteral RPAREN
#traversalMethod_aggregate_String
@@ -558,7 +557,7 @@ traversalMethod_not
traversalMethod_option
: 'option' LPAREN traversalPredicate COMMA nestedTraversal RPAREN
#traversalMethod_option_Predicate_Traversal
- | 'option' LPAREN traversalMerge COMMA genericLiteralMap RPAREN
#traversalMethod_option_Merge_Map
+ | 'option' LPAREN traversalMerge COMMA (genericLiteralMap |
nullLiteral) RPAREN #traversalMethod_option_Merge_Map
| 'option' LPAREN traversalMerge COMMA nestedTraversal RPAREN
#traversalMethod_option_Merge_Traversal
| 'option' LPAREN genericLiteral COMMA nestedTraversal RPAREN
#traversalMethod_option_Object_Traversal
| 'option' LPAREN nestedTraversal RPAREN
#traversalMethod_option_Traversal
diff --git a/gremlin-test/features/map/MergeVertex.feature
b/gremlin-test/features/map/MergeVertex.feature
index 4707555..7201433 100644
--- a/gremlin-test/features/map/MergeVertex.feature
+++ b/gremlin-test/features/map/MergeVertex.feature
@@ -64,7 +64,123 @@ Feature: Step - mergeV()
# g_V_mapXmergeXlabel_person_name_joshXX
# - mergeV(Map) with no option() - testing child traversal usage
# - results in one new vertex and one existing vertex that was just created
+ # g_mergeVXnullX
+ # - mergeV(null) with no option()
+ # - results in no new vertex and nothing returned
+ # g_mergeVXemptyX
+ # - mergeV(empty) with no option()
+ # - results in matched vertex with no updates
+ # g_mergeVXemptyX_no_existing
+ # - mergeV(empty) with no option()
+ # - results in not matched updates and a creation of a vertex with default
values
+ # g_mergeVXnullX_optionXonCreate_emptyX
+ # - mergeV(null) with onCreate(empty)
+ # - results in no matches and creates a default vertex
+ # g_mergeVXlabel_person_name_stephenX_optionXonCreate_nullX
+ # - mergeV(Map) with onCreate(null)
+ # - results in no match and no vertex creation
+ # g_mergeVXnullX_optionXonCreate_label_null_name_markoX
+ # - mergeV(null) with onCreate(Map) where Map has a null label
+ # - results in error
+ # g_mergeVXemptyX_optionXonMatch_nullX
+ # - mergeV(empty) with onMatch(null)
+ # - results in a match and no vertex update
+ Scenario: g_mergeVXemptyX_optionXonMatch_nullX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And the traversal of
+ """
+ g.mergeV([:]).option(Merge.onMatch, null)
+ """
+ When iterated to list
+ Then the result should have a count of 1
+ And the graph should return 1 for count of
"g.V().has(\"person\",\"name\",\"marko\").has(\"age\",29)"
+
+ Scenario: g_mergeVXnullX_optionXonCreate_label_null_name_markoX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And using the parameter xx1 defined as "m[{\"t[label]\": null,
\"name\":\"marko\"}]"
+ And the traversal of
+ """
+ g.mergeV(null).option(Merge.onCreate,xx1)
+ """
+ When iterated to list
+ Then the traversal will raise an error
+
+ Scenario: g_mergeVXlabel_person_name_stephenX_optionXonCreate_nullX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And using the parameter xx1 defined as "m[{\"t[label]\": \"person\",
\"name\":\"stephen\"}]"
+ And the traversal of
+ """
+ g.mergeV(xx1).option(Merge.onCreate, null)
+ """
+ When iterated to list
+ Then the result should have a count of 0
+ And the graph should return 1 for count of "g.V()"
+ And the graph should return 1 for count of
"g.V().has(\"person\",\"name\",\"marko\")"
+
+ Scenario: g_mergeVXnullX_optionXonCreate_emptyX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And the traversal of
+ """
+ g.mergeV(null).option(Merge.onCreate,[:])
+ """
+ When iterated to list
+ Then the result should have a count of 1
+ And the graph should return 2 for count of "g.V()"
+
+ Scenario: g_mergeVXemptyX_no_existing
+ Given the empty graph
+ And the traversal of
+ """
+ g.mergeV([:])
+ """
+ When iterated to list
+ Then the result should have a count of 1
+ And the graph should return 1 for count of "g.V()"
+
+ Scenario: g_mergeVXemptyX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And the traversal of
+ """
+ g.mergeV([:])
+ """
+ When iterated to list
+ Then the result should have a count of 1
+ And the graph should return 1 for count of
"g.V().has(\"person\",\"name\",\"marko\").has(\"age\",29)"
+
+ Scenario: g_mergeVXnullX
+ Given the empty graph
+ And the graph initializer of
+ """
+ g.addV("person").property("name", "marko").property("age", 29)
+ """
+ And the traversal of
+ """
+ g.mergeV(null)
+ """
+ When iterated to list
+ Then the result should have a count of 0
+ And the graph should return 1 for count of "g.V()"
Scenario: g_mergeVXlabel_person_name_stephenX
Given the empty graph
diff --git
a/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/traversal/step/map/TinkerMergeVertexStep.java
b/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/traversal/step/map/TinkerMergeVertexStep.java
index 6771ebd..9c3cc03 100644
---
a/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/traversal/step/map/TinkerMergeVertexStep.java
+++
b/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/traversal/step/map/TinkerMergeVertexStep.java
@@ -52,7 +52,9 @@ public class TinkerMergeVertexStep<S> extends
MergeVertexStep<S> {
Stream<Vertex> stream;
// prioritize lookup by id but otherwise attempt an index lookup
- if (search.containsKey(T.id)) {
+ if (null == search) {
+ return Stream.empty();
+ } else if (search.containsKey(T.id)) {
stream = IteratorUtils.stream(graph.vertices(search.get(T.id)));
} else {
// look for the first index we can find - that's the lucky winner.
may or may not be the most selective
