NullPointerException error message - Designer Cloud

[TracyB513]

I recreated a workflow that hadn't been working due to an AMP error.  It ran fine yesterday.  Today I tried to run the same workflow without changing any of the date and I am getting an error message: NullPointerException.  I went through and cleaned the data at every step replacing any nulls that might exist with '0' or blank spaces.  I am still getting the error message.  I don't know what my next step would be to troubleshoot.  Has anyone experienced this before?

[TracyB513]

I rebuilt my workflow using the same data - I didn't change a thing - and it works fine.  I think my real test will be whether it runs fine the next day.