Symbol getStringBufferAppend(JCTree tree, Type t) {
            assert t.constValue() == null;
            Symbol method = stringBufferAppend.get(t);
            if (method == null) {
                method = rs.resolveInternalMethod(tree.pos(),
                                                  attrEnv,
                                                  stringBufferType,
                                                  names.append,
                                                  List.of(t),
                                                  null);
                stringBufferAppend.put(t, method);
            }
            return method;
        }