What to do if an Assembly Step hasn’t produced any results?

Please double check the following:

Is your Step's Robot able to deal with the file you are providing it with? The video related robots, for example, will ignore all files except videos.
Does the Step referenced in your Step's use parameter produce any result? Are you sure that your Step actually has some input?
If the result of your Step is passed into a subsequent Step, it will not produce a result by default. You can add result: true to your Step to force the creation of a result in this case.