code: public static PropertyFile readOnlyUnion(final PropertyFile... files)
  	{
  		final PropertyFile props = new PropertyFile();
  
  		for (PropertyFile file : files)
  		{
  			if (file != null)
  				props.merge(file);
  		}
  
  		props.makeReadOnly();
  
  		return props;
  	}
docs: Construct a new read-only PropertyFile which merges the contents of a number of other PropertyFile objects<br />
  Null PropertyFiles are ignored.
  
  @param files
  
  @return