use head on push if sha empty?

Author: plowsof

.github/workflows/ci.yml

@@ -83,6 +83,10 @@ jobs:
             echo "DEBUG: push"
             BASE_SHA=$GITHUB_EVENT_BEFORE
           fi
+          if [[ -z "$BASE_SHA" ]]; then
+            echo "branch doesnt exist? using HEAD^"
+            BASE_SHA=$(git rev-parse HEAD^)
+          fi
           echo "BASE_SHA=$BASE_SHA" >> $GITHUB_ENV
           echo "Using BASE_SHA=$BASE_SHA"