Print NULL as "(null)" in diagnostic message
Passing a null pointer to the printf family for a %s format specifier leads to undefined behaviour. The tests currently expect (null). Explicitly test for a null pointer and provide the expected string.
Authored By: andusy
Reviewers: hubert.reinterpretcast, xingxue, jasonliu, daltenty, cebowleratibm
Reviewed By: hubert.reinterpretcast
Subscribers: arphaman, jsji, cfe-commits
Differential Revision: https://reviews.llvm.org/D63786