code: static BigqueryFieldMarshaller findMarshaller(Field field,
        Map<Field, BigqueryFieldMarshaller> marshallers) {
      BigqueryFieldMarshaller marshaller = null;
      if (marshallers != null) {
        marshaller = marshallers.get(field);
      }
      if (marshaller == null) {
        marshaller = BigqueryFieldMarshallers.getMarshaller(field.getType());
      }
      return marshaller;
    }
docs: Returns if a {@link BigqueryFieldMarshaller} exists for the field either in the map provided or
  the internally maintained list.