On Friday our production log system alerted us that we had an error ("dash lengths all zero, ignored"). We investigated and found that the PDF processed gave an error when opening it up in Adobe Reader as well but the page looked fine and was processed fine as well. But still we got this error. For us this is a false positive, even though a line pattern should not be empty the page isn't broken or can't be viewed so why handle it as an error.
My suggestion is to handle the errors in the code below as an information logging or warning.
In our case we got an update 1 hour later with a PDF that didn't have the empty line dash pattern.