toPreprocessorTriggerTransformer = function ( target, targetProperty, value) {

	if( !target.defines ) return;

	if ( value ) {

		if( target.defines[targetProperty] === undefined ) {

			target.defines[targetProperty] = '';
			target.needsUpdate = true;

		}

	} else if( target.defines[targetProperty] !== undefined ) {

		delete target.defines[targetProperty];
		target.needsUpdate = true;

	}

}
Transform a value as a preprocessor trigger
@type {import('../Mediator').MediationTransformer}