with "Git validated merge support" enabled
with Build Triggers "Build when a change is pushed to GitHub" and "GitHub Pull Request Builder" enabled with Admin list specified

with build trigger of pull request from non-admin user, following is the build output

GitHub pull request #3 to daya/testing-jenkins
Building in workspace /Users/dayas/.jenkins/jobs/testing-jenkins/workspace
> /usr/local/bin/git rev-parse --is-inside-work-tree # timeout=10
Fetching changes from the remote Git repository
> /usr/local/bin/git config remote.origin.url https://github.com/daya/testing-jenkins/ # timeout=10
Fetching upstream changes from https://github.com/daya/testing-jenkins/
> /usr/local/bin/git --version # timeout=10
using .gitcredentials to set credentials
[WARNING] Installed git version too old for credentials support
> /usr/local/bin/git config --local credential.helper store --file=/Users/Shared/Jenkins/tmp/git8378518816609888499.credentials # timeout=10
> /usr/local/bin/git fetch --tags --progress https://github.com/daya/testing-jenkins/ +refs/heads/master:refs/remotes/origin/master
> /usr/local/bin/git config --local --remove-section credential # timeout=10
> /usr/local/bin/git config core.sparsecheckout # timeout=10
> /usr/local/bin/git checkout -f origin/master # timeout=10
> /usr/local/bin/git branch -a # timeout=10
> /usr/local/bin/git rev-parse master^

{commit} # timeout=10
> /usr/local/bin/git rev-parse remotes/origin/master^{commit}

# timeout=10
> /usr/local/bin/git branch -D master # timeout=10
> /usr/local/bin/git checkout -b master origin/master
Opening connection
Done: 0
Counting objects
Done: 3
Finding sources
Done: 3
Getting sizes
Done: 2
Compressing objects
Done: 287
Writing objects
Done: 3
remote: Updating references
Merging refs/tags/changes/10
> /usr/local/bin/git rev-parse refs/tags/changes/10^

{commit} # timeout=10
> /usr/local/bin/git merge 59090368c94a33dc7e8544e4b3161aabc3ef8643 # timeout=10
> /usr/local/bin/git rev-parse master^{commit}

# timeout=10
Checking out Revision 59090368c94a33dc7e8544e4b3161aabc3ef8643 (master)
> /usr/local/bin/git config core.sparsecheckout # timeout=10
> /usr/local/bin/git checkout -f 59090368c94a33dc7e8544e4b3161aabc3ef8643
> /usr/local/bin/git rev-parse origin/master^

{commit}

# timeout=10
> /usr/local/bin/git rev-list 7be695dac6701671360e2764ff784ec5f65f8ec7 # timeout=10
[workspace] $ /bin/sh -xe /Users/Shared/Jenkins/tmp/hudson407296555273413991.sh
+ BRANCH=
+ ./sleep.sh
sleeping for 15 seconds

woke up after 15 seconds
Putting comment on the pull request
ERROR: Failed to update the ticket
java.io.FileNotFoundException: /Users/dayas/.github (No such file or directory)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(FileInputStream.java:146)
at java.io.FileInputStream.<init>(FileInputStream.java:101)
at org.kohsuke.github.GitHubBuilder.fromPropertyFile(GitHubBuilder.java:32)
at org.kohsuke.github.GitHubBuilder.fromPropertyFile(GitHubBuilder.java:26)
at org.kohsuke.github.GitHub.connect(GitHub.java:134)
at com.cloudbees.jenkins.plugins.github_pull.TicketUpdater.onCompleted(TicketUpdater.java:54)
at com.cloudbees.jenkins.plugins.github_pull.TicketUpdater.onCompleted(TicketUpdater.java:23)
at hudson.model.listeners.RunListener.fireCompleted(RunListener.java:199)
at hudson.model.Run.execute(Run.java:1796)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:89)
at hudson.model.Executor.run(Executor.java:240)
Finished: SUCCESS