CompoundExpression omits null-safe syntax in AST string representation of null-safe selection/projection in SpEL

[sbrannen]

The AST string representations of the following SpEL expressions currently omit the null-safe navigation operator (?.) that was present in the original expression.

• null-safe projection: {1,2,3}?.![#isEven()] --> {1,2,3}.![#isEven()]
• null-safe selection: {1,2,3}?.?[#isEven(#this)] --> {1,2,3}.?[#isEven(#this)]
• null-safe select first: {1,2,3}?.^[#isEven(#this)] --> {1,2,3}.^[#isEven(#this)]
• null-safe select last: {1,2,3}?.$[#isEven(#this)] --> {1,2,3}.$[#isEven(#this)]