docs: def get_change_type(self, ref, a1, a2):
          """
          Given ref, allele1, and allele2, returns the type of change.
          The only case of an amino acid insertion is when the ref is
          represented as a '.'.
          """
          if ref == '.':
              return self.INSERTION
          elif a1 == '.' or a2 == '.':
              return self.DELETION