Suppose I have

file_spec_a = 'path_to_files_a/*.nc'
file_spec_b = 'path_to_files_b/*.nc'

if file_spec_b doesn't point to any existing files, then iris.load([file_spec_a, file_spec_b]) rightly produces an exception in iris.io.expand_filespecs. However, the exception message includes all the filenames matching file_spec_a, as well as telling me that file_spec_b expanded to empty. This can sometimes be a lot of output, which I have to search through to find the "empty" so I can fix the problem. Could this exception message be reduced to only list the file specifications which don't expand?