Fix an edge case with custom error printing.
Fix an edge case with custom error printing.

andene/substance,abhaga/substance,michael/substance-1,TypesetIO/substance,TypesetIO/substance,michael/substance-1,abhaga/substance,andene/substance,podviaznikov/substance,podviaznikov/substance,stencila/substance,jacwright/substance,substance/substance,jacwright/substance,substance/substance