code: private static void checkPreconditions(final Map<Object, Object> mapping) {
  		if( mapping == null ) {
  			throw new NullPointerException("mapping should not be null");
  		} else if( mapping.isEmpty() ) {
  			throw new IllegalArgumentException("mapping should not be empty");
  		}
  	}
docs: Checks the preconditions for creating a new HashMapper processor.
  
  @param mapping
  the Map
  @throws NullPointerException
  if mapping is null
  @throws IllegalArgumentException
  if mapping is empty