code: public <T> T getFieldNotNull(int pos){
  		T field = getField(pos);
  		if (field != null) {
  			return field;
  		} else {
  			throw new NullFieldException(pos);
  		}
  	}
docs: Gets the field at the specified position, throws NullFieldException if the field is null. Used for comparing key fields.
  
  @param pos The position of the field, zero indexed.
  @return The field at the specified position.
  @throws IndexOutOfBoundsException Thrown, if the position is negative, or equal to, or larger than the number of fields.
  @throws NullFieldException Thrown, if the field at pos is null.