fix(CI): fix PR compliance test when diff is empty

.github/workflows/CI.yml

@@ -56,7 +56,12 @@ jobs:
         pip install pylint
         PR_BRANCH=${{ github.event.pull_request.target.ref }}
         MAIN_BRANCH=origin/${{ github.event.pull_request.base.ref }}
-        MESSAGE=$(pylint -ry --disable=E0401 `git diff --name-only --diff-filter=d $MAIN_BRANCH $PR_BRANCH | grep -E '\.py$' | tr '\n' ' '` ||:)
+        CURRENT_DIFF=$(git diff --name-only --diff-filter=d $MAIN_BRANCH $PR_BRANCH  | grep -E '\.py$' | tr '\n' ' ')
+        if [[ $CURRENT_DIFF == "" ]];
+          then MESSAGE="Diff is empty and there is nothing to pylint."
+        else
+          MESSAGE=$(pylint -ry --disable=E0401 $CURRENT_DIFF ||:)
+        fi
         echo 'MESSAGE<<EOF' >> $GITHUB_ENV
         echo "<pre><code>$MESSAGE</code></pre>" >> $GITHUB_ENV
         echo 'EOF' >> $GITHUB_ENV