SpEL Compiler: NPE on Indexer compilation, when is used map accessor [SPR-12045]

[spring-projects-issues]

Artem Bilan opened SPR-12045 and commented

The expression looks like headers[command],
#root is the same org.springframework.messaging.Message
The StackTrace:

Caused by: java.lang.NullPointerException
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.generateCode(PropertyOrFieldReference.java:337)
	at org.springframework.expression.spel.ast.Indexer.generateCode(Indexer.java:264)
	at org.springframework.expression.spel.ast.CompoundExpression.generateCode(CompoundExpression.java:133)
	at org.springframework.expression.spel.standard.SpelCompiler.createExpressionClass(SpelCompiler.java:154)
	at org.springframework.expression.spel.standard.SpelCompiler.compile(SpelCompiler.java:104)
	at org.springframework.expression.spel.standard.SpelExpression.compileExpression(SpelExpression.java:464)
	at org.springframework.expression.spel.standard.SpelExpression.checkCompile(SpelExpression.java:434)
	at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:328)

Changing expression to this headers['command'] fix the issue.

Thanks

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Affects: 4.1 RC1

Referenced from: commits 813cc3b

[spring-projects-issues]

Andy Clement commented

All fixed up. The primary problem here is that the handling of the special case of an unquoted key in an indexer was not being also done in the generateCode() method for the indexer. In the expression "headers[command]" where the key is not quoted it is actually parsed as a PropertyOrFieldReference node. There is then special handling during map access that recognizes this situation and just retrieves the name of the PropertyOrFieldReference node, rather than evaluating it. Without that special handling in code generation we were attempting to generate code for that 'fake' PropertyOrFieldReference and raising an NPE.