check for first commit

.github/workflows/registry-updates.yaml

@@ -16,8 +16,20 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v2
 
+      - name: Check if it's the first commit on branch
+        id: check_first_commit
+        run: |
+          if [ "${{ github.event.before }}" == "0000000000000000000000000000000000000000" ]; then
+            echo "::set-output name=first_commit::true"
+          else
+            echo "::set-output name=first_commit::false"
+          fi
+
       - name: List changed files
         id: list_files
         run: |
-          git diff --name-only ${{ github.event.before }} ${{ github.event.after }} > changed_files.txt
-
+          if [ "${{ steps.check_first_commit.outputs.first_commit }}" == "true" ]; then
+            git ls-tree --name-only -r ${{ github.sha }} > changed_files.txt
+          else
+            git diff --name-only ${{ github.event.before }} ${{ github.sha }} > changed_files.txt
+          fi