<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _first_fill_value_loc(self):
 """ Get the location of the first missing value. Returns ------- int """

        if len(self) == 0 or self.sp_index.npoints == len(self):
            return -1

        indices = self.sp_index.to_int_index().indices
        if not len(indices) or indices[0] > 0:
            return 0

        diff = indices[1:] - indices[:-1]
        return np.searchsorted(diff, 2) + 1