gitTags: ignore repos with no tags.

lib/package-managers/gitTags.js

@@ -18,7 +18,7 @@ const greatest = async (name, version, options) => {
   }
   // catch a variety of errors that occur on invalid or private repos
   catch (e) {
-    print(options, `Invalid or Private repo ${name}: ${version}`, 'verbose')
+    print(options, `Invalid, private repo, or no tags for ${name}: ${version}`, 'verbose')
     return null
   }
 
@@ -28,7 +28,9 @@ const greatest = async (name, version, options) => {
     .filter(semver.valid)
     .sort(versionUtil.compareVersions)
   const latestVersion = tags[tags.length - 1]
-  return versionUtil.upgradeGithubUrl(version, latestVersion)
+  return latestVersion
+    ? versionUtil.upgradeGithubUrl(version, latestVersion)
+    : null
 }
 
 module.exports = {

test/test-versionmanager.js

@@ -519,7 +519,15 @@ describe('versionmanager', () => {
         })
       })
 
-      it('private github urls with tags should be ignored', async () => {
+      it('ignore repos with no tags', async () => {
+        const upgrades = await vm.queryVersions({
+          // this repo has tag "1.0" which is not valid semver
+          'ncu-test-invalid-tag': 'git+https://github.com/raineorshine/ncu-test-no-tags#v1'
+        }, { loglevel: 'silent' })
+        upgrades.should.deep.equal({})
+      })
+
+      it('valid but non-existent github urls with tags should be ignored', async () => {
         const upgrades = await vm.queryVersions({
           'ncu-test-alpha': 'git+https://username:dh9dnas0nndnjnjasd4@bitbucket.org/somename/common.git#v283',
           'ncu-test-private': 'https://github.com/ncu-test/ncu-test-private#v999.9.9',