fix(manager:regex): allow no match in combination (#11386)

lib/manager/regex/index.spec.ts

@@ -240,6 +240,20 @@ describe('manager/regex/index', () => {
     expect(res.deps).toHaveLength(1);
   });
 
+  it('extracts with combination strategy and empty file', async () => {
+    const config: CustomExtractConfig = {
+      matchStringsStrategy: 'combination',
+      matchStrings: [
+        'CHART_REPOSITORY_URL: "(?<registryUrl>.*)\\/(?<depName>[a-z]+)\\/"',
+        'CHART_VERSION: (?<currentValue>.*?)\n',
+      ],
+      datasourceTemplate: 'helm',
+      depNameTemplate: 'helm_repo/{{{ depName }}}',
+    };
+    const res = await extractPackageFile('', '.gitlab-ci.yml', config);
+    expect(res).toBeNull();
+  });
+
   it('extracts with recursive strategy and single match', async () => {
     const config: CustomExtractConfig = {
       matchStrings: [

lib/manager/regex/index.ts

@@ -147,12 +147,17 @@ function handleCombination(
     .map((matchString) => regEx(matchString, 'g'))
     .flatMap((regex) => regexMatchAll(regex, content)); // match all regex to content, get all matches, reduce to single array
 
+  if (!matches.length) {
+    return [];
+  }
+
   const combinedGroup = matches
     .map((match) => match.groups)
     .reduce((mergedGroup, currentGroup) =>
       mergeGroups(mergedGroup, currentGroup)
     );
 
+  // TODO: this seems to be buggy behavior, needs to be checked #11387
   const dep = matches
     .map((match) => createDependency(match, combinedGroup, config))
     .reduce(