public static UFreeIdent create(CharSequence identifier) {
    return new AutoValue_UFreeIdent(StringName.of(identifier));
  }
@Test
  public void binds() {
    JCExpression expr = parseExpression("\"abcdefg\".charAt(x + 1)");
    UFreeIdent ident = UFreeIdent.create("foo");
    assertThat(ident.unify(expr, unifier)).isNotNull();
    assertThat(unifier.getBindings()).containsExactly(new UFreeIdent.Key("foo"), expr);
  }