code: def is_missing(self):
          
  
          out = np.any(self.values < 0, axis=-1)
  
          # handle mask
          if self.mask is not None:
              out |= self.mask
  
          return out
docs: Find missing genotype calls.
  
          Returns
          -------
          out : ndarray, bool, shape (n_variants, n_samples)
              Array where elements are True if the genotype call matches the
              condition.
  
          Examples
          --------
  
          >>> import allel
          >>> g = allel.GenotypeArray([[[0, 0], [0, 1]],
          ...                          [[0, 1], [1, 1]],
          ...                          [[0, 2], [-1, -1]]])
          >>> g.is_missing()
          array([[False, False],
                 [False, False],
                 [False,  True]])
          >>> v = g[:, 1]
          >>> v
          <GenotypeVector shape=(3, 2) dtype=int64>
          0/1 1/1 ./.
          >>> v.is_missing()
          array([False, False,  True])