Add default value for message Resolution

According to the spec [1] the Resolution is required,
but in the generator code it's added only if it's defined
in the source. Use default value "None." if it's not defined.

[1] https://redfish.dmtf.org/schemas/v1/MessageRegistry.v1_6_3.json

Change-Id: I91ac6504c69bc2c0f0018a6e39a67563079fc983
Signed-off-by: Igor Kanyuka <ifelmail@gmail.com>
diff --git a/tools/sdbusplus/event.py b/tools/sdbusplus/event.py
index 0dedefb..e843d4c 100644
--- a/tools/sdbusplus/event.py
+++ b/tools/sdbusplus/event.py
@@ -75,6 +75,8 @@
         result["Message"] = language_data.message
         if language_data.resolution:
             result["Resolution"] = language_data.resolution
+        else:
+            result["Resolution"] = "None."
 
         result["MessageSeverity"] = self.registry_sev