buildbot exception in MacPorts on ports-10.11_x86_64-watcher

[buildbot at macports.org]

The Buildbot has detected a build exception on builder ports-10.11_x86_64-watcher while building macports/macports-ports. Full details are available at:
    https://build.macports.org/builders/ports-10.11_x86_64-watcher/builds/31600

Buildbot URL: https://build.macports.org/

Buildslave for this Build: ports-10.11_x86_64

Build Reason: The SingleBranchScheduler scheduler named 'ports' triggered this build
Build Source Stamp: [branch master] c8083a967b3b5d87ca1f2e3b4033343b010f94c7
Blamelist: Chris Jones <jonesc at macports.org>

BUILD FAILED: exception

Sincerely,
 -The Buildbot