I have a Jenkins jobs setup to poll SCM nightly and run a build if there are changes. The problem is if there are no changes, Jenkins executes the job anyway.

Here is console output of a simple job that polls SCM and then executes a single build step (shell command of "echo blah").

attached is a screenshot of the console output (also available here: http://i.imgur.com/5jQTIAe.png)

You can see, even though there were no SCM changes, the build continues. The behavior I am looking for is if there is no change, the build steps are not executed. Also strange is the first thing in the output is "Started by an SCM change", followed by an indication that there was in fact no change.