skip over undefined properties in rules

see regression https://github.com/webpack/webpack/issues/8537#issuecomment-508451734

lib/rules/RuleSetCompiler.js

@@ -140,7 +140,9 @@ class RuleSetCompiler {
 	 * @returns {CompiledRule} normalized and compiled rule for processing
 	 */
 	compileRule(path, rule, refs) {
-		const unhandledProperties = new Set(Object.keys(rule));
+		const unhandledProperties = new Set(
+			Object.keys(rule).filter(key => rule[key] !== undefined)
+		);
 
 		/** @type {CompiledRule} */
 		const compiledRule = {

test/configCases/rule-set/undefined-values/index.js

@@ -0,0 +1 @@
+it("compile fine", () => {});

test/configCases/rule-set/undefined-values/webpack.config.js

@@ -0,0 +1,13 @@
+module.exports = {
+	module: {
+		rules: [
+			{
+				test: undefined,
+				loader: undefined,
+				use: undefined,
+				options: undefined,
+				resource: undefined
+			}
+		]
+	}
+};