How to catch errors in mendix?

When I run the program, and click on a specific page, I occasionally get the error message  Error An error occurred, please contact your system administrator. However, the results of the page is still the same. So how do I remove this error? From my experience of java code, you can catch the error and do some other actions instead of showing an error. I don’t really understand the documentation.   Here is the microflow if anyone wants it.         And the error code: Did not expect an argument to be undefined Error: Did not expect an argument to be undefined  
1 answers

That message usually means something is “empty”, maybe the retrieve or REST call isn’t returning something? The best way to find out is to single step through the microflow and check the variables at each stage. 

Hope this helps.