Avoid setting baseUrl to undefined when input is not provided

.github/workflows/integration.yml

@@ -248,3 +248,78 @@ jobs:
           done <<< "$tests"
 
           echo $'\u2705 Test passed' | tee -a $GITHUB_STEP_SUMMARY
+
+  test-base-url:
+    name: 'Integration test: base-url option'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ./.github/actions/install-dependencies
+
+      - id: base-url-default
+        name: API URL with base-url not set
+        uses: ./
+        with:
+          script: |
+            const endpoint = github.request.endpoint
+            return endpoint({}).url
+          result-encoding: string
+
+      - id: base-url-default-graphql
+        name: GraphQL URL with base-url not set
+        uses: ./
+        with:
+          script: |
+            const endpoint = github.request.endpoint
+            return endpoint({url: "/graphql"}).url
+          result-encoding: string
+
+      - id: base-url-set
+        name: API URL with base-url set
+        uses: ./
+        with:
+          base-url: https://my.github-enterprise-server.com/api/v3
+          script: |
+            const endpoint = github.request.endpoint
+            return endpoint({}).url
+          result-encoding: string
+
+      - id: base-url-set-graphql
+        name: GraphQL URL with base-url set
+        uses: ./
+        with:
+          base-url: https://my.github-enterprise-server.com/api/v3
+          script: |
+            const endpoint = github.request.endpoint
+            return endpoint({url: "/graphql"}).url
+          result-encoding: string
+
+      - run: |
+          echo "- Validating API URL default"
+          expected="https://api.github.com/"
+          actual="${{steps.base-url-default.outputs.result}}"
+          if [[ "$expected" != "$actual" ]]; then
+            echo $'::error::\u274C' "Expected base-url to equal '$expected', got $actual"
+            exit 1
+          fi
+          echo "- Validating GraphQL URL default"
+          expected="https://api.github.com/graphql"
+          actual="${{steps.base-url-default-graphql.outputs.result}}"
+          if [[ "$expected" != "$actual" ]]; then
+            echo $'::error::\u274C' "Expected base-url to equal '$expected', got $actual"
+            exit 1
+          fi
+          echo "- Validating base-url set to a value"
+          expected="https://my.github-enterprise-server.com/api/v3/"
+          actual="${{steps.base-url-set.outputs.result}}"
+          if [[ "$expected" != "$actual" ]]; then
+            echo $'::error::\u274C' "Expected base-url to equal '$expected', got $actual"
+            exit 1
+          fi
+          echo "- Validating GraphQL URL with base-url set to a value"
+          expected="https://my.github-enterprise-server.com/api/v3/graphql"
+          actual="${{steps.base-url-set-graphql.outputs.result}}"
+          if [[ "$expected" != "$actual" ]]; then
+            echo $'::error::\u274C' "Expected base-url to equal '$expected', got $actual"
+            exit 1
+          fi