import-index: Fix for require() (#436)

Author: garyking

rules/import-index.js

@@ -6,7 +6,7 @@ const isImportingIndex = value => regexp.test(value);
 const normalize = value => value.replace(regexp, '$1');
 
 const importIndex = (context, node, argument) => {
-	if (isImportingIndex(argument.value)) {
+	if (argument && isImportingIndex(argument.value)) {
 		context.report({
 			node,
 			message: 'Do not reference the index file directly.',

test/import-index.js

@@ -18,6 +18,7 @@ const error = {
 
 ruleTester.run('import-index', rule, {
 	valid: [
+		'const m = require()',
 		'const m = require(\'.\')',
 		'const m = require(\'..\')',
 		'const m = require(\'../..\')',