FIX: skip adding sso diagnostics if sso object is nil

app/controllers/session_controller.rb

@@ -116,7 +116,7 @@ class SessionController < ApplicationController
       sso = DiscourseSingleSignOn.parse(request.query_string)
     rescue DiscourseSingleSignOn::ParseError => e
       if SiteSetting.verbose_sso_logging
-        Rails.logger.warn("Verbose SSO log: Signature parse error\n\n#{e.message}\n\n#{sso.diagnostics}")
+        Rails.logger.warn("Verbose SSO log: Signature parse error\n\n#{e.message}\n\n#{sso&.diagnostics}")
       end
 
       # Do NOT pass the error text to the client, it would give them the correct signature