If there is a performance implication of moving the if into the callers or not, you can do it with an inline function.

  static inline int function(blob *ptr, int arg)
  {
     if (ptr == NULL)
       return ERR_NULL;
     return real_function(ptr, arg);
  }

Just like that, we effectively moved the if statement into 37 callers, where the compiler may be smart enough to hoist it out of a for loop when it sees that the pointer is never changed in the loop body, or to eliminate it entirely when it sees that the pointer cannot be null.