skip empty description

Don't print the description of a command as a subtitle
when generating a manpage if the description is empty.
This commit addresses #9430

Signed-off-by: Harumi Kuno <harumi.kuno@hpe.com>

sphinx/writers/manpage.py

@@ -113,8 +113,9 @@ def __init__(self, document: nodes.document, builder: Builder) -> None:
     def header(self) -> str:
         tmpl = (".TH \"%(title_upper)s\" \"%(manual_section)s\""
                 " \"%(date)s\" \"%(version)s\" \"%(manual_group)s\"\n"
-                ".SH NAME\n"
-                "%(title)s \\- %(subtitle)s\n")
+                ".SH NAME\n")
+        if self._docinfo['subtitle']:
+            tmpl += "%(title)s \\- %(subtitle)s\n"
         return tmpl % self._docinfo
 
     def visit_start_of_file(self, node: Element) -> None: