fix: better fix for undefined new docker digest

lib/manager/docker/package.js

@@ -148,13 +148,15 @@ async function getPackageUpdates(config) {
           config.depName,
           upgrade.newTag
         );
-        if (!upgrade.newDigest) {
+        if (upgrade.newDigest) {
+          upgrade.newFrom += `@${upgrade.newDigest}`;
+        } else {
           logger.warn(
             { dockerRegistry, depName, tag: upgrade.newTag },
             'Dockerfile no digest'
           );
+          upgrade.newDigest = undefined;
         }
-        upgrade.newFrom += `@${upgrade.newDigest}`;
       }
       if (newVersionMajor > currentMajor) {
         upgrade.type = 'major';
@@ -170,7 +172,7 @@ async function getPackageUpdates(config) {
       );
     }
   }
-  return upgrades.filter(u => u.newDigest !== null);
+  return upgrades;
 }
 
 function isStable(tag, unstablePattern) {

test/manager/docker/__snapshots__/package.spec.js.snap

@@ -14,7 +14,7 @@ Array [
     "isMinor": true,
     "newDepTag": "some-dep:1.1.0-something",
     "newDigest": undefined,
-    "newFrom": "some-dep:1.1.0-something@undefined",
+    "newFrom": "some-dep:1.1.0-something",
     "newTag": "1.1.0-something",
     "newVersion": "1.1.0-something",
     "newVersionMajor": "1",