docs: def source_headers(self):
          """"Returns the headers for the resource source. Specifically, does not include any header that is
          the EMPTY_SOURCE_HEADER value of _NONE_"""
  
          t = self.schema_term
  
          if t:
              return [self._name_for_col_term(c, i)
                      for i, c in enumerate(t.children, 1) if c.term_is("Table.Column")
                      and c.get_value('name') != EMPTY_SOURCE_HEADER
                      ]
          else:
              return None