When employees enter expense reports, they can (but are not systematically required to) enter a project number for the report. The workflow uses this value to determine the project manager to approve the report if that branch of the workflow is initiated. However, this value is not available to the workflow itself, so we are unable to test it to determine if there is a value present. This means that if an employee leaves it blank, the workflow will fail with an error that it is impossible for us to trap for. Microsoft has determined this is "working as designed" and indicated we should file an idea here for them to consider correcting this behavior.