See http://www.netbeans.org/issues/show_bug.cgi?id=158634

We often get NPE at ReferenceTypeImpl.constantPool(ReferenceTypeImpl.java:1025):

java.lang.NullPointerException
        at com.sun.tools.jdi.ReferenceTypeImpl.constantPool(ReferenceTypeImpl.java:1025)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:0)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
Caused: java.lang.IllegalStateException: java.lang.NullPointerException
        at org.netbeans.modules.debugger.jpda.jdi.ReferenceTypeWrapper.constantPool(ReferenceTypeWrapper.java:227)
        at org.netbeans.modules.debugger.jpda.ExpressionPool.createExpressionAt(ExpressionPool.java:168)
        at org.netbeans.modules.debugger.jpda.ExpressionPool.getExpressionAt(ExpressionPool.java:102)
        at org.netbeans.modules.debugger.jpda.actions.MethodChooser.collectOperations(MethodChooser.java:306)
        at org.netbeans.modules.debugger.jpda.actions.MethodChooser.run(MethodChooser.java:189)
        at org.netbeans.modules.debugger.jpda.actions.StepIntoActionProvider.doMethodSelection(StepIntoActionProvider.java:170)
        at org.netbeans.modules.debugger.jpda.actions.StepIntoActionProvider.runAction(StepIntoActionProvider.java:114)
        at org.netbeans.modules.debugger.jpda.actions.StepIntoActionProvider$1.run(StepIntoActionProvider.java:105)
        at org.netbeans.modules.debugger.jpda.actions.JPDADebuggerActionProvider$1.run(JPDADebuggerActionProvider.java:169)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:573)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1005)

Looking into the code, cpbytes is null. It's taken from constantPoolBytesRef.get(), which can return null, since constantPoolBytesRef is a SoftReference.