Make docker build target optional

.github/workflows/docker-build-publish.yml

@@ -114,9 +114,14 @@ jobs:
               BUILD_ARG_FLAGS=$(printf -- "--build-arg %s " $BUILD_ARGS)
             fi
 
+            TARGET_FLAG=""
+            if [ -n "$TARGET" ] && [ "$TARGET" != "null" ]; then
+              TARGET_FLAG="--target $TARGET"
+            fi
+
             docker buildx build \
               --file "$DOCKERFILE" \
-              --target "$TARGET" \
+              $TARGET_FLAG \
               --cache-from "type=registry,ref=$CACHE_REF" \
               --cache-to "type=registry,ref=$CACHE_REF,mode=max" \
               $SSH_FLAGS \