🚀 go-pugleaf

I have tried to run through the second example in jbuilder 2005 database tutorial several times and always come up with the same problem.  The tutorial says to make a certain field calculated. When I do this, it generates an error having to do with a CalcFieldsListener and from then on I cannot get back into the designeer.  In looking at the source, I also cannot figure out how to correct the error that was generated by the designer change.  So, in situations where the designer causes an error, how are we to fix this?  Why does opening a designer require error free code?  It seems to me that once an error is created, the designers should still open.  I am posting this in the documentation area because I suspect that either the tutorial left something out or I just am too new to the whole subject (true).