Do I need to ldap_memfree after ldap_get_lderrno? SDK docs say yes.

Some basic questions about ldap_get_lderrno:

- Do I have to call ldap_memfree for either *m or *s? Code example 5-6 
in the SDK documentation calls ldap_memfree to release the error string 
after printing it. Do I have to call it for both?
- Can I pass NULL for either/both *m and *s? The SDK documentation 
doesn't explain whether I can pass NULL for a string I don't want.
- Will I get LDAP_SUCCESS if there is no "last" error?

Thanks!
- Matthew