fix: check that required arguments are set (#8)

Fixes MRGFY-3942

action.yml

@@ -36,6 +36,17 @@ runs:
       run: |
         set -x
 
+        # Check if FILES and MERGIFY_CI_ISSUES_TOKEN are set and not empty
+        if [ -z "$FILES" ]; then
+          echo "::error:: report_paths is not set or is empty"
+          exit 1
+        fi
+
+        if [ -z "$MERGIFY_CI_ISSUES_TOKEN" ]; then
+          echo "::error:: token is not set or is empty"
+          exit 1
+        fi
+
         # TODO(sileht): support multiple files
         curl -X POST \
           -H "Authorization: bearer ${MERGIFY_CI_ISSUES_TOKEN}" \