@Test
public void conv_missing_value() {

  FunctionExpression conv = dsl.conv(
      DSL.ref(STRING_TYPE_MISSING_VALUE_FILED, STRING), DSL.literal(10), DSL.literal(2));
  assertEquals(STRING, conv.type());
  assertTrue(conv.valueOf(valueEnv()).isMissing());
  conv = dsl.conv(
      DSL.literal("1"), DSL.ref(INT_TYPE_MISSING_VALUE_FIELD, INTEGER), DSL.literal(2));
  assertEquals(STRING, conv.type());
  assertTrue(conv.valueOf(valueEnv()).isMissing());
  conv = dsl.conv(
      DSL.literal("1"), DSL.literal(10), DSL.ref(INT_TYPE_MISSING_VALUE_FIELD, INTEGER));
  assertEquals(STRING, conv.type());
  assertTrue(conv.valueOf(valueEnv()).isMissing());
}