Fix printing None if no publication for entry

No adding an empty string to the resulting markdown instead of the
actual content of the dict ('None') to the text.

processing/content.py

@@ -18,7 +18,7 @@ def experience_to_md(data: dict[str, Any], lang: str = "en", headline: str = "")
         md += f"## {exp['title'][lang]}\\hfill{exp['date'][lang]}\n\n"
 
         if "publication" in exp:
-            md += f"> {exp['publication'][lang]}\n\n"
+            md += f"> {exp['publication'][lang] or ''}\n\n"
 
         for point in exp["bullets"]:
             md += f"* {point[lang]}\n"