--- a/src/Pure/Thy/bibtex.scala Fri Feb 24 20:40:50 2023 +0100
+++ b/src/Pure/Thy/bibtex.scala Fri Feb 24 20:52:35 2023 +0100
@@ -680,7 +680,7 @@
"\"$BIB2XHTML_HOME/main/bib2xhtml.pl\" -B \"$ISABELLE_BIBTEX\"" +
" -u -s " + Bash.string(proper_string(style) getOrElse "empty") +
(if (chronological) " -c" else "") +
- (if (title != "") " -h " + Bash.string(title) + " " else "") +
+ if_proper(title, " -h " + Bash.string(title) + " ") +
" " + File.bash_path(in_file) + " " + File.bash_path(out_file),
cwd = tmp_dir.file).check