Merge pull request #41533 from MikeEdgar/fix-image-registry-npe

Avoid NPE handling registry in image reference parsing

extensions/container-image/spi/src/main/java/io/quarkus/container/spi/ImageReference.java

@@ -147,32 +147,29 @@ public static ImageReference parse(String reference) {
         String tag = matcher.group(3);
         String digest = matcher.group(4);
 
-        // If no registry was matched, use Docker Hub by default.
-        if (StringUtil.isNullOrEmpty(registry)) {
-            registry = null;
-        }
-
         if (StringUtil.isNullOrEmpty(repository)) {
             throw new IllegalArgumentException("Reference " + reference + " is invalid: The repository was not set");
         }
-        /*
-         * If a registry was matched but it does not contain any dots or colons, it should actually be
-         * part of the repository unless it is "localhost".
-         *
-         * See https://github.com/docker/distribution/blob/245ca4659e09e9745f3cc1217bf56e946509220c/reference/normalize.go#L62
-         */
-        if (!registry.contains(".") && !registry.contains(":") && !"localhost".equals(registry)) {
+
+        if (StringUtil.isNullOrEmpty(registry)) {
+            registry = null;
+        } else if (!registry.contains(".") && !registry.contains(":") && !"localhost".equals(registry)) {
+            /*
+             * If a registry was matched but it does not contain any dots or colons, it should actually be
+             * part of the repository unless it is "localhost".
+             *
+             * See
+             * https://github.com/docker/distribution/blob/245ca4659e09e9745f3cc1217bf56e946509220c/reference/normalize.go#L62
+             */
             repository = registry + "/" + repository;
             registry = null;
-        }
-
-        /*
-         * For Docker Hub, if the repository is only one component, then it should be prefixed with
-         * 'library/'.
-         *
-         * See https://docs.docker.com/engine/reference/commandline/pull/#pull-an-image-from-docker-hub
-         */
-        if (DOCKER_HUB_REGISTRY.equals(registry) && repository.indexOf('/') < 0) {
+        } else if (DOCKER_HUB_REGISTRY.equals(registry) && repository.indexOf('/') < 0) {
+            /*
+             * For Docker Hub, if the repository is only one component, then it should be prefixed with
+             * 'library/'.
+             *
+             * See https://docs.docker.com/engine/reference/commandline/pull/#pull-an-image-from-docker-hub
+             */
             repository = LIBRARY_REPOSITORY_PREFIX + repository;
         }