fix: undefined when source map undefined

Author: evilebottnawi

lib/loader.js

@@ -129,7 +129,7 @@ module.exports = function(content, map) {
 		// embed runtime
 		callback(null, "exports = module.exports = require(" +
 			loaderUtils.stringifyRequest(this, require.resolve("./css-base.js")) +
-			")(" + query.sourceMap + ");\n" +
+			")(" + query.sourceMap ? query.sourceMap : "" + ");\n" +
 			"// imports\n" +
 			importJs + "\n\n" +
 			"// module\n" +