[gi-docgen/ebassi/deprecated-no-msg] gir: Do not require a deprecation message

[Emmanuele Bassi <ebassi src gnome org>]

commit ae40a75e6a638865ea2a27bd9aa908c7fcbff56e
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Jan 20 14:15:58 2022 +0000

    gir: Do not require a deprecation message
    
    Symbols can be deprecated with just a version identifier, even though it
    is preferable to have a message.

 gidocgen/gir/parser.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/gidocgen/gir/parser.py b/gidocgen/gir/parser.py
index 823b111..aa42502 100644
--- a/gidocgen/gir/parser.py
+++ b/gidocgen/gir/parser.py
@@ -333,8 +333,9 @@ class GirParser:
         if deprecated is not None:
             deprecated_since = node.attrib.get('deprecated-version')
             deprecated_doc = self._maybe_parse_deprecated_doc(node)
-            if deprecated_doc is not None:
-                element.set_deprecated(deprecated_doc, deprecated_since)
+            if deprecated_doc is None:
+                deprecated_doc = ''
+            element.set_deprecated(deprecated_doc, deprecated_since)
 
     def _parse_array(self, node: ET.Element) -> ast.Type:
         child = node.find('core:array', GI_NAMESPACES)