Some input filesystems don't implement purge

Author: halfnelson

lib/virtual.js

@@ -12,7 +12,9 @@ function VirtualModulesPlugin(compiler) {
 		var originalPurge = compiler.inputFileSystem.purge;
 
 		compiler.inputFileSystem.purge = function() {
-			originalPurge.call(this, arguments);
+			if (originalPurge) {
+				originalPurge.call(this, arguments);
+			}
 			if (this._virtualFiles) {
 				Object.keys(this._virtualFiles).forEach(
 					function(file) {