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/25163

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] 2c259ef62f7d0c27336182e8c9416ca3d7e3e254
Blamelist: Chris Jones <jonesc at macports.org>

BUILD FAILED: exception

Sincerely,
 -The Buildbot