Error with perfect fit

[VLDrenth]

When either the mediator or independent variable is the same as the dependent variable, the GUI crashes when running a model, with console warning:

 S-estimated scale == 0:  Probably exact fit; check your data 
Warning in seq_len(ar) : first element used of 'length.out' argument
Warning: Error in numeric: invalid 'length' argument

[aalfons]

The GUI should catch errors and warnings when executing test_mediation() and then give a more helpful message in the main panel that lists a few common issues and suggestions (e.g., check for missing values or other issues of the data, try increasing the number of bootstrap samples, etc.).