Revert "Add callIfNull support"

This reverts commit 5dd62e2836.

index.js

@@ -3,13 +3,9 @@
 const combinator = require("@validatem/combinator");
 
 module.exports = function withContext(rules, context) {
-	let validator = combinator((item, applyValidators, parentContext) => {
+	return combinator((item, applyValidators, parentContext) => {
 		let mergedContext = Object.assign({}, parentContext, context);
 		
 		return applyValidators(item, rules, mergedContext);
 	});
-
-	validator.callIfNull = true;
-
-	return validator;
 };