Handle null branch

.github/actions/commit-range/action.yml

@@ -50,16 +50,26 @@ runs:
               --head ${{ github.ref_name }} \
               --json number,baseRefName \
               --limit 1)
-          if [[ -n "$pr_info" ]]; then
+          if [[ \
+              -n "$pr_info" && \
+              "$(echo "$pr_info" | jq '.[0].baseRefName')" != "null" \
+          ]]; then
             base_branch=$(echo "$pr_info" | jq -r '.[0].baseRefName')
-            echo "Associated PR found."
+            echo "Associated PR found. Base branch: ${base_branch}"
           else
-            echo "No associated PR found. Using default branch as base."
+            echo "No associated PR found or base branch is null."
+            echo "Using default branch as base."
             base_branch=$(gh api repos/${{ github.repository }} --jq '.default_branch')
+            echo "Default branch: ${base_branch}"
           fi
-          echo "Base branch: ${base_branch}"
 
-          branch_point=$(git merge-base origin/${base_branch} ${{ github.sha }})
+          echo "Fetching the branch point..."
+          if ! branch_point=$(git merge-base origin/${base_branch} ${{ github.sha }})
+          then
+            echo "Failed to find merge-base."
+            echo "Using the first commit of the current branch."
+            branch_point=$(git rev-list --max-parents=0 HEAD)
+          fi
           echo "Branch point: ${branch_point}"
 
           range="${branch_point}...${{ github.sha }}"