code: @Override
      public SourcePosition position() {
          if (sym.enclClass().sourcefile == null) return null;
          return SourcePositionImpl.make(sym.enclClass().sourcefile,
                                         (tree==null) ? 0 : tree.pos,
                                         lineMap);
      }
docs: Return the source position of the entity, or null if
  no position is available.