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new c9872f3727 Issue #4373 : Keep JSON null distinct from an empty string
(#8691)
c9872f3727 is described below
commit c9872f37277aba3d4d1854dffad63a2b482dcb2e
Author: Matt Casters <[email protected]>
AuthorDate: Thu Oct 1 12:01:45 2026 +0200
Issue #4373 : Keep JSON null distinct from an empty string (#8691)
---
.../jsoninput/reader/RowOutputConverter.java | 7 ++
.../transforms/jsoninput/JsonInputTest.java | 107 +++++++++++++++++++++
2 files changed, 114 insertions(+)
diff --git
a/plugins/transforms/json/src/main/java/org/apache/hop/pipeline/transforms/jsoninput/reader/RowOutputConverter.java
b/plugins/transforms/json/src/main/java/org/apache/hop/pipeline/transforms/jsoninput/reader/RowOutputConverter.java
index 2fd9bd6e23..d10b266987 100644
---
a/plugins/transforms/json/src/main/java/org/apache/hop/pipeline/transforms/jsoninput/reader/RowOutputConverter.java
+++
b/plugins/transforms/json/src/main/java/org/apache/hop/pipeline/transforms/jsoninput/reader/RowOutputConverter.java
@@ -51,6 +51,13 @@ public class RowOutputConverter {
}
// convert from string
String strValue = getStringValue(value);
+ if (strValue == null) {
+ // JSON null and a missing path are null. convertDataFromString turns a
null string into ""
+ // when HOP_EMPTY_STRING_DIFFERS_FROM_NULL is Y, which hides the
difference between "" and
+ // null. An empty JSON string ("") is not null and still goes through
conversion below.
+ // See Apache Hop #4373.
+ return null;
+ }
return targetMeta.convertDataFromString(
strValue, strConvertMeta, null, null, targetMeta.getTrimType());
}
diff --git
a/plugins/transforms/json/src/test/java/org/apache/hop/pipeline/transforms/jsoninput/JsonInputTest.java
b/plugins/transforms/json/src/test/java/org/apache/hop/pipeline/transforms/jsoninput/JsonInputTest.java
index cff1953d93..da7199790c 100644
---
a/plugins/transforms/json/src/test/java/org/apache/hop/pipeline/transforms/jsoninput/JsonInputTest.java
+++
b/plugins/transforms/json/src/test/java/org/apache/hop/pipeline/transforms/jsoninput/JsonInputTest.java
@@ -19,6 +19,7 @@ package org.apache.hop.pipeline.transforms.jsoninput;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.when;
@@ -42,6 +43,7 @@ import java.util.zip.ZipOutputStream;
import org.apache.commons.io.IOUtils;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystemException;
+import org.apache.hop.core.Const;
import org.apache.hop.core.HopClientEnvironment;
import org.apache.hop.core.IRowSet;
import org.apache.hop.core.exception.HopException;
@@ -1898,4 +1900,109 @@ class JsonInputTest {
assertTrue(results.contains("three"));
}
}
+
+ /**
+ * Issue #4373. With HOP_EMPTY_STRING_DIFFERS_FROM_NULL=Y a JSON {@code
null} (and a missing path)
+ * must stay null, while {@code ""} stays an empty string. Otherwise both
come out as "".
+ */
+ @Test
+ void testEmptyStringDiffersFromJsonNull() throws Exception {
+ ParsedRows parsed = readEmptyAndNullRows("Y");
+ List<Object[]> rows = parsed.rows;
+ IValueMeta tenantName = parsed.rowMeta.searchValueMeta("tenantName");
+ // {"params":{},"tenantName":"hop"} — jobNumber is absent
+ assertNull(rows.get(0)[1]);
+ assertEquals("{}", rows.get(0)[2]);
+ assertEquals("hop", rows.get(0)[3]);
+ // {"jobNumber":3,"params":{},"tenantName":null}
+ assertEquals("3", rows.get(1)[1]);
+ assertEquals("{}", rows.get(1)[2]);
+ assertNull(rows.get(1)[3]);
+ assertTrue(tenantName.isNull(rows.get(1)[3]));
+ // {"jobNumber":2,"tenantName":""} — params is absent, tenantName is empty
+ assertEquals("2", rows.get(2)[1]);
+ assertNull(rows.get(2)[2]);
+ assertEquals("", rows.get(2)[3]);
+ assertFalse(tenantName.isNull(rows.get(2)[3]));
+ // {"jobNumber":120,"params":{},"tenantName":"hop"}
+ assertEquals("120", rows.get(3)[1]);
+ assertEquals("{}", rows.get(3)[2]);
+ assertEquals("hop", rows.get(3)[3]);
+ // {"jobNumber":1,"params":{}} — tenantName is absent
+ assertEquals("1", rows.get(4)[1]);
+ assertEquals("{}", rows.get(4)[2]);
+ assertNull(rows.get(4)[3]);
+ assertTrue(tenantName.isNull(rows.get(4)[3]));
+ }
+
+ /**
+ * Default (the variable is N): an empty string is still stored as "", but
it compares as null, so
+ * preview shows both as {@code <null>}. JSON null and a missing path stay
null.
+ */
+ @Test
+ void testEmptyStringAndJsonNullLookTheSameByDefault() throws Exception {
+ ParsedRows parsed = readEmptyAndNullRows("N");
+ List<Object[]> rows = parsed.rows;
+ assertNull(rows.get(1)[3]);
+ assertEquals("", rows.get(2)[3]);
+ assertNull(rows.get(0)[1]);
+ assertNull(rows.get(2)[2]);
+ assertNull(rows.get(4)[3]);
+
+ IValueMeta tenantName = parsed.rowMeta.searchValueMeta("tenantName");
+ assertTrue(tenantName.isNull(rows.get(1)[3]));
+ assertTrue(tenantName.isNull(rows.get(2)[3]));
+ }
+
+ private ParsedRows readEmptyAndNullRows(String emptyDiffersFromNull) throws
Exception {
+ String previous =
System.getProperty(Const.HOP_EMPTY_STRING_DIFFERS_FROM_NULL);
+ System.setProperty(Const.HOP_EMPTY_STRING_DIFFERS_FROM_NULL,
emptyDiffersFromNull);
+ try {
+ JsonInputField jobNumber = new JsonInputField("jobNumber");
+ jobNumber.setPath("$.jobNumber");
+ jobNumber.setType(IValueMeta.TYPE_STRING);
+ JsonInputField params = new JsonInputField("params");
+ params.setPath("$.params");
+ params.setType(IValueMeta.TYPE_STRING);
+ JsonInputField tenantName = new JsonInputField("tenantName");
+ tenantName.setPath("$.tenantName");
+ tenantName.setType(IValueMeta.TYPE_STRING);
+
+ JsonInputMeta meta = createSimpleMeta("content", jobNumber, params,
tenantName);
+ JsonInput transform =
+ createJsonInput(
+ "content",
+ meta,
+ new Object[] {"{\"params\":{},\"tenantName\":\"hop\"}"},
+ new Object[]
{"{\"jobNumber\":3,\"params\":{},\"tenantName\":null}"},
+ new Object[] {"{\"jobNumber\":2,\"tenantName\":\"\"}"},
+ new Object[]
{"{\"jobNumber\":120,\"params\":{},\"tenantName\":\"hop\"}"},
+ new Object[] {"{\"jobNumber\":1,\"params\":{}}"});
+
+ ParsedRows parsed = new ParsedRows();
+ transform.addRowListener(
+ new RowAdapter() {
+ @Override
+ public void rowWrittenEvent(IRowMeta rowMeta, Object[] row) {
+ parsed.rowMeta = rowMeta;
+ parsed.rows.add(row);
+ }
+ });
+ processRows(transform, 10);
+ assertEquals(0, transform.getErrors());
+ assertEquals(5, parsed.rows.size());
+ return parsed;
+ } finally {
+ if (previous == null) {
+ System.clearProperty(Const.HOP_EMPTY_STRING_DIFFERS_FROM_NULL);
+ } else {
+ System.setProperty(Const.HOP_EMPTY_STRING_DIFFERS_FROM_NULL, previous);
+ }
+ }
+ }
+
+ private static final class ParsedRows {
+ private final List<Object[]> rows = new ArrayList<>();
+ private IRowMeta rowMeta;
+ }
}
