Early return if this build is from a forked PR

.circleci/config.yml

@@ -2,14 +2,27 @@
 #
 # Check https://circleci.com/docs/2.0/language-java/ for more details
 #
-version: 2
+version: 2.1
+
+commands:
+  early_return_for_forked_pull_requests:
+    description: >-
+      If this build is from a fork, stop executing the current job and return success.
+      This is useful to avoid steps that will fail due to missing credentials.
+    steps:
+      - run:
+          name: Early return if this build is from a forked PR
+          command: |
+            if [ -n "$CIRCLE_PR_NUMBER" ]; then
+              echo "Nothing to do for forked PRs, so marking this step successful"
+              circleci step halt
+            fi
+
 jobs:
   build:
     docker:
       - image: circleci/openjdk:8u171-jdk
-
       - image: redislabs/rejson:edge
-        port: 6379:6379
 
     working_directory: ~/repo
 
@@ -37,6 +50,7 @@ jobs:
 
       # run tests!
       - run: mvn integration-test
+      - early_return_for_forked_pull_requests
       - run: mvn cobertura:cobertura
       - run: bash <(curl -s https://raw.githubusercontent.com/codecov/codecov-bash/master/codecov) -t ${CODECOV_TOKEN}