allow optional CN in reissue and clone

lemur/certificates/schemas.py

@@ -369,6 +369,11 @@ def handle_subject_details(self, data):
             if field in data and data[field] is None:
                 data.pop(field)
 
+        # Earlier common_name was a required field and thus in most places there is no None check for it.
+        # Now that it is optional, setting value as empty string instead of None for backward compatibility
+        if data.get("common_name") is None:
+            data["common_name"] = ""
+
 
 class CertificateShortOutputSchema(LemurOutputSchema):
     id = fields.Integer()