Issue fabric8io#1185 Prevent docker:save failing when no images are d…

…efined.

Signed-off-by: William Rose <william.rose@nuance.com>

src/main/java/io/fabric8/maven/docker/SaveMojo.java

@@ -44,6 +44,9 @@ protected void executeInternal(ServiceHub serviceHub) throws DockerAccessExcepti
 			return;
 		}
 		String imageName = getImageName();
+		if(imageName == null) {
+			return;
+		}
 		String fileName = getFileName(imageName);
 		ensureSaveDir(fileName);
 		log.info("Saving image %s to %s", imageName, fileName);
@@ -101,6 +104,10 @@ private String getImageName() throws MojoExecutionException {
 		// specify image by name or alias
 		if (saveName == null && saveAlias == null) {
 			List<ImageConfiguration> buildImages = getImagesWithBuildConfig(images);
+			if (buildImages.isEmpty()) {
+				log.info("No images have a build configuration defined: save skipped");
+				return null;
+			}
 			if (buildImages.size() == 1) {
                 return buildImages.get(0).getName();
 			}