None does not compare to int

Change-Id: Ia1542e40faa4a49d00289eec7717a0f5a47122fc
diff --git a/zuul/model.py b/zuul/model.py
index 8284b03..12f08ae 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -1235,7 +1235,7 @@
         del self.node_requests[job_name]
 
     def getTries(self, job_name):
-        return self.tries.get(job_name)
+        return self.tries.get(job_name, 0)
 
     def getMergeMode(self):
         if self.layout: