Suspected bug, expected PropertyAccessException but got NPE.

[elevenching]

I am not sure if this is a bug, but I encountered this situation while using the software. It does not occur consistently.

For an expression like "$.result.success," the data being accessed might have a "result" value or not. After compiling the expression using MVEL.compileExpression, I use MVEL.executeExpression to obtain the value. If the current data does not have a "result" value, I expect it to throw a PropertyAccessException, but instead, I get a NullPointerException (NPE).

Upon tracing the code, I found a suspicious part.

In ASTNode, there is a variable "protected transient volatile Accessor accessor;" with the "volatile" modifier. When I try to execute the expression from data without a "result" value and trace it to ASTNode, I find that the accessor already exists. As a result, it attempts to access the values in the order of "$," "result," and "success." Since "result" does not exist, it throws an NPE.

Actually, the expectation was that the accessor would not exist, and during the construction of the accessor, a PropertyAccessException would be thrown due to the null "result" value.

Therefore, I suspect that the issue is caused by the "volatile" modifier, which makes the accessor visible to other threads during concurrent execution, leading to the problem described above.

[linux2014linux]

@elevenching Could you provide some example code?