code: public int getListFieldLength(String fieldName) {
  		int ret = -1;
  		Object val = getFieldValue(fieldName, true); // internal
  		if (val instanceof List<?>)
  			ret = ((List<?>)val).size();
  		else if (val != null && val.getClass().isArray()) {
  			ret = Array.getLength(val);
  		} else {
  			if (!getDomainObjectType().getFieldByName(fieldName).isListOrArray())
  				throw new RuntimeException("field: [" + fieldName + "] is neither list nor array");
  			if (val == null)
  				throw new RuntimeException("list or array field: [" + fieldName + "] is null");
  		}
  		return ret;
  	}
docs: Answer the length of a list field
  @param fieldName
  @return