code: private Schema readEnum(JsonReader reader) throws IOException {
      if (!"symbols".equals(reader.nextName())) {
        throw new IOException("Property \"symbols\" missing for enum.");
      }
      ImmutableList.Builder<String> enumValues = ImmutableList.builder();
      reader.beginArray();
      while (reader.peek() != JsonToken.END_ARRAY) {
        enumValues.add(reader.nextString());
      }
      reader.endArray();
      return Schema.enumWith(enumValues.build());
    }
docs: Constructs {@link Schema.Type#ENUM ENUM} type schema from the json input.
  
  @param reader The {@link JsonReader} for streaming json input tokens.
  @return A {@link Schema} of type {@link Schema.Type#ENUM ENUM}.
  @throws java.io.IOException When fails to construct a valid schema from the input.