Return value of function, which is statistically inferred to return null, but with no source code available, is dereferenced

Defect 50827 (STATIC_C)
Checker NULL_RETURNS (subcategory unimpl)
File: /src/os_common/os_errno.c
Function __wt_errno
/src/os_common/os_errno.c, line: 22
Assuming unimplemented function "__errno_location" may return a null value.

    	return (errno == 0 ? WT_ERROR : errno);

/src/os_common/os_errno.c, line: 22
Dereferencing "__errno_location()", which is known to be "NULL".

    	return (errno == 0 ? WT_ERROR : errno);