Allow rule.create to return undefined (#1912)

Author: fisker

rules/filename-case.js

@@ -147,7 +147,7 @@ const create = context => {
 	const filenameWithExtension = context.getPhysicalFilename();
 
 	if (filenameWithExtension === '<input>' || filenameWithExtension === '<text>') {
-		return {};
+		return;
 	}
 
 	return {

rules/no-empty-file.js

@@ -20,7 +20,7 @@ const create = context => {
 	const filename = context.getPhysicalFilename().toLowerCase();
 
 	if (!/\.(?:js|mjs|cjs|ts|mts|cts)$/.test(filename)) {
-		return {};
+		return;
 	}
 
 	return {

rules/prefer-module.js

@@ -218,7 +218,7 @@ function create(context) {
 	const filename = context.getFilename().toLowerCase();
 
 	if (filename.endsWith('.cjs')) {
-		return {};
+		return;
 	}
 
 	const sourceCode = context.getSourceCode();

rules/string-content.js

@@ -70,7 +70,7 @@ const create = context => {
 	const replacements = getReplacements(patterns);
 
 	if (replacements.length === 0) {
-		return {};
+		return;
 	}
 
 	return {

rules/utils/rule.js

@@ -71,10 +71,18 @@ function reportProblems(create) {
 		return create;
 	}
 
-	const wrapped = context => Object.fromEntries(
-		Object.entries(create(context))
-			.map(([selector, listener]) => [selector, reportListenerProblems(listener, context)]),
-	);
+	const wrapped = context => {
+		const listeners = create(context);
+
+		if (!listeners) {
+			return {};
+		}
+
+		return Object.fromEntries(
+			Object.entries(listeners)
+				.map(([selector, listener]) => [selector, reportListenerProblems(listener, context)]),
+		);
+	};
 
 	wrappedFunctions.add(wrapped);