protected static boolean isNull(Object val) {
    return (val == null) || STRING_NULL.equals(val) || DOUBLE_NULL.equals(val) || INTEGER_NULL.equals(val);
  }
protected static boolean isNull ( Object val ) { return ( val == null ) || STRING_NULL . equals ( val ) || DOUBLE_NULL . equals ( val ) || INTEGER_NULL . equals ( val ) ; }
Test a value for null.

TODO: delegate to {@link FeatureVector} instead?

@param val Value
@return true when null