LLDB's output may be None instead of '', and that will cause type
mismatch when normalize_whitespace() expects a string instead of
None. This commit simply ensures we do pass '' even if the output
is None.
Right now on the most recent version of LLDB installed on OSX we'll segfault on
all the LLDB tests if this isn't called (unfortunately). Hopefully we've updated
LLDB on the bots to actually get this working everywhere!
Closes#32994
