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https://issues.apache.org/jira/browse/TAPESTRY-1648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540083
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Christian E Gruber commented on TAPESTRY-1648:
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A null value is not a number, but it is not a string, it is the absence of a
value. But, the absence of a value is a meaningful state. That is why RDBMSs
include "tri state logic". The whole theory of nulls in software is that the
absence of a value is not the same thing as a value with a default number. If
you want to implement your logic to never have null values, then make all your
objects init with defaults, but Java supports nulls and so Tapestry, which is a
Java framework, should not make assumptions that are different than the Java
language.
Integer i = null;
Integer i = 0;
These are different, and should be distinguishable. Especially because null is
often an error state and shoudl be testable wihtout having to guard each and
every situation with a null pointer exception trap.
Since textfields and selections hold string labels/values, it is reasonable
that when coercing a null number into such a field, that you coerce it into the
empty string, or soemthing similar, not a number 0 which has mathematical
meaning that is calculable. Null means not calculable, in a sense. And when
coercing a null back into a number, if it's a number object (Integer/Boolean,
etc.) then should pass in as a null. If it's a primitive type that doesn't
support nulls, then it should go to a default value like 0/false, because there
you don't have a choice, in my view.
> Coercing from null to BigDecimal causes an NPE
> ----------------------------------------------
>
> Key: TAPESTRY-1648
> URL: https://issues.apache.org/jira/browse/TAPESTRY-1648
> Project: Tapestry
> Issue Type: Bug
> Components: tapestry-ioc
> Affects Versions: 5.0.5
> Reporter: Dan Adams
> Assignee: Howard M. Lewis Ship
> Priority: Blocker
> Fix For: 5.0.6
>
>
> I'm working on a currency textfield for bigdecimal and I get this exception
> because it tries to coerce from null to String (which returns null) and then
> passes a null into the BigDecimal(String) constructor which causes the NPE.
> org.apache.tapestry.ioc.internal.util.TapestryException: Failure reading
> parameter value of component CurrencyFieldTestPage:value: Coercion of null to
> type java.math.BigDecimal (via null --> String, String -->
> java.math.BigDecimal) failed: java.lang.NullPointerException [at
> classpath:com/ifactory/cms/cms/integration/app0/pages/CurrencyFieldTestPage.html,
> line 5, column 78]
> at
> org.apache.tapestry.internal.structure.ComponentPageElementImpl.invoke(ComponentPageElementImpl.java:935)
> at
> org.apache.tapestry.internal.structure.ComponentPageElementImpl.access$100(ComponentPageElementImpl.java:69)
> at
> org.apache.tapestry.internal.structure.ComponentPageElementImpl$10.render(ComponentPageElementImpl.java:349)
> at
> org.apache.tapestry.internal.services.RenderQueueImpl.run(RenderQueueImpl.java:57)
> at
> org.apache.tapestry.internal.services.PageMarkupRendererImpl.renderPageMarkup(PageMarkupRendererImpl.java:40)
> at
> $PageMarkupRenderer_113c1389a35.renderPageMarkup($PageMarkupRenderer_113c1389a35.java)
> at
> org.apache.tapestry.internal.services.PageResponseRendererImpl.renderPageResponse(PageResponseRendererImpl.java:71)
> at
> $PageResponseRenderer_113c13899fc.renderPageResponse($PageResponseRenderer_113c13899fc.java)
> at
> org.apache.tapestry.internal.services.PageRenderRequestHandlerImpl.handle(PageRenderRequestHandlerImpl.java:81)
> at
> $PageRenderRequestHandler_113c13899f1.handle($PageRenderRequestHandler_113c13899f1.java)
> at
> org.apache.tapestry.internal.test.PageLinkInvoker.invoke(PageLinkInvoker.java:57)
> at org.apache.tapestry.test.PageTester.invoke(PageTester.java:184)
> at org.apache.tapestry.test.PageTester.renderPage(PageTester.java:144)
> at
> com.ifactory.cms.cms.components.CurrencyFieldTest.testFormatting(CurrencyFieldTest.java:23)
> Caused by: org.apache.tapestry.ioc.internal.util.TapestryException: Failure
> reading parameter value of component CurrencyFieldTestPage:value: Coercion of
> null to type java.math.BigDecimal (via null --> String, String -->
> java.math.BigDecimal) failed: java.lang.NullPointerException
> at
> org.apache.tapestry.internal.structure.InternalComponentResourcesImpl.readParameter(InternalComponentResourcesImpl.java:210)
> at
> com.ifactory.cms.cms.components.CurrencyField._$read_parameter_value(CurrencyField.java)
> at
> com.ifactory.cms.cms.components.CurrencyField.beginRender(CurrencyField.java:109)
> at
> com.ifactory.cms.cms.components.CurrencyField.beginRender(CurrencyField.java)
> at
> org.apache.tapestry.internal.structure.ComponentPageElementImpl$10$1.run(ComponentPageElementImpl.java:345)
> at
> org.apache.tapestry.internal.structure.ComponentPageElementImpl.invoke(ComponentPageElementImpl.java:931)
> ... 34 more
> Caused by: java.lang.RuntimeException: Coercion of null to type
> java.math.BigDecimal (via null --> String, String --> java.math.BigDecimal)
> failed: java.lang.NullPointerException
> at
> org.apache.tapestry.ioc.internal.services.TypeCoercerImpl.coerce(TypeCoercerImpl.java:154)
> at $TypeCoercer_113c13899e0.coerce($TypeCoercer_113c13899e0.java)
> at
> org.apache.tapestry.internal.structure.InternalComponentResourcesImpl.readParameter(InternalComponentResourcesImpl.java:206)
> ... 39 more
> Caused by: java.lang.NullPointerException
> at java.math.BigDecimal.<init>(BigDecimal.java:594)
> at
> org.apache.tapestry.ioc.services.TapestryIOCModule$7.coerce(TapestryIOCModule.java:219)
> at
> org.apache.tapestry.ioc.services.TapestryIOCModule$7.coerce(TapestryIOCModule.java:217)
> at
> org.apache.tapestry.ioc.services.CoercionTuple$CoercionWrapper.coerce(CoercionTuple.java:53)
> at
> org.apache.tapestry.ioc.internal.services.CompoundCoercion.coerce(CompoundCoercion.java:48)
> at
> org.apache.tapestry.ioc.internal.services.TypeCoercerImpl.coerce(TypeCoercerImpl.java:150)
> ... 41 more
> ... Removed 21 stack frames
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