[DROOLS-7428] ErrorUtil should not throw NPE

[tkobayas]

https://kie.zulipchat.com/#narrow/stream/232678-jbpm/topic/WorkItemHandler

https://issues.redhat.com/browse/DROOLS-7428

The problem is that ErrorUtil throws NPE when caught.getExpr() is null, so the call cannot get the root cause of the CompileException.

It is reported for business-central, but this should be fixed for general use cases.

[tkobayas]

The test failure seems to be caused by the use of OptimizerFactory.setDefaultOptimizer("ASM"). Not related to this PR. We will need to address it in a separated JIRA/PR (e.g write common setUp to enable OptimizerFactory.DYNAMIC). -> filed https://issues.redhat.com/browse/DROOLS-7429

2023-04-28T09:15:38.8694781Z Tests run: 318, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 1.158 sec <<< FAILURE! - in org.mvel2.tests.core.CoreConfidenceTests
2023-04-28T09:15:38.8712458Z testMapAccessProperty(org.mvel2.tests.core.CoreConfidenceTests)  Time elapsed: 0.001 sec  <<< ERROR!
2023-04-28T09:15:38.8716465Z org.mvel2.CompileException: [Error: [Error: could not access: key; in class: java.util.HashMap]
2023-04-28T09:15:38.8717135Z [Near : {... map.key ....}]
2023-04-28T09:15:38.8717593Z              ^
2023-04-28T09:15:38.8718074Z [Line: 1, Column: 1]]
2023-04-28T09:15:38.8718375Z [Near : {... map.key ....}]
2023-04-28T09:15:38.8718660Z              ^
2023-04-28T09:15:38.8718935Z [Line: 1, Column: 1]
2023-04-28T09:15:38.8719437Z    at org.mvel2.optimizers.impl.asm.ASMAccessorOptimizer.getBeanProperty(ASMAccessorOptimizer.java:1332)
2023-04-28T09:15:38.8720270Z    at org.mvel2.optimizers.impl.asm.ASMAccessorOptimizer.compileAccessor(ASMAccessorOptimizer.java:856)
2023-04-28T09:15:38.8720996Z    at org.mvel2.optimizers.impl.asm.ASMAccessorOptimizer.optimizeAccessor(ASMAccessorOptimizer.java:345)
2023-04-28T09:15:38.8721583Z    at org.mvel2.ast.ASTNode.optimize(ASTNode.java:159)
2023-04-28T09:15:38.8722083Z    at org.mvel2.ast.ASTNode.getReducedValueAccelerated(ASTNode.java:115)
2023-04-28T09:15:38.8722897Z    at org.mvel2.compiler.ExecutableAccessor.getValue(ExecutableAccessor.java:42)
2023-04-28T09:15:38.8723444Z    at org.mvel2.MVEL.executeExpression(MVEL.java:970)
2023-04-28T09:15:38.8724331Z    at org.mvel2.tests.core.CoreConfidenceTests.testMapAccessProperty(CoreConfidenceTests.java:3502)