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

Defect 103846 (STATIC_C)
Checker NULL_RETURNS (subcategory unimpl)
File: /bench/wtperf/config.c
Function config_opt_file
/bench/wtperf/config.c, line: 515
Assuming unimplemented function "__ctype_b_loc" may return a null value.

    		for (ltrim = line; *ltrim && isspace((u_char)*ltrim);

/bench/wtperf/config.c, line: 515
Dereferencing "__ctype_b_loc()", which is known to be "NULL".

    		for (ltrim = line; *ltrim && isspace((u_char)*ltrim);

File: /bench/wtperf/config.c
Function config_opt_file
/bench/wtperf/config.c, line: 535
Assuming unimplemented function "__ctype_b_loc" may return a null value.

    		while (rtrim > ltrim && isspace((u_char)rtrim[-1]))

/bench/wtperf/config.c, line: 535
Dereferencing "__ctype_b_loc()", which is known to be "NULL".

    		while (rtrim > ltrim && isspace((u_char)rtrim[-1]))

File: /bench/wtperf/config.c
Function config_opt_file
/bench/wtperf/config.c, line: 555
Assuming unimplemented function "__ctype_b_loc" may return a null value.

    		while (rtrim > ltrim && isspace((u_char)rtrim[-1]))

/bench/wtperf/config.c, line: 555
Dereferencing "__ctype_b_loc()", which is known to be "NULL".

    		while (rtrim > ltrim && isspace((u_char)rtrim[-1]))