diff --git a/chipathlon/workflow.py b/chipathlon/workflow.py
index 0c8417de19b6d3b6abf73ca03601a6c8a66dd93e..0c2f9cd15fac3053875e40a4a7c632398573ebe9 100644
--- a/chipathlon/workflow.py
+++ b/chipathlon/workflow.py
@@ -157,6 +157,9 @@ class Workflow(object):
             with open(self.param_file, "r") as rh:
                 try:
                     self.params = yaml.load(rh)
+                    if self.params is None:
+                        print "[WARNING] Param file is empty.  Using defaults for all jobs."
+                        self.params = {}
                 except yaml.YAMLError as ye:
                     self.errors.append("Error parsing param yaml file '%s': %s." % (self.param_file, ye))
         else:
@@ -209,7 +212,7 @@ class Workflow(object):
                 run.load_samples(self.mdb)
             self.runs = self.run_parser.get_runs()
         else:
-            self.err += self.run_parser.get_error_string()
+            self.errors.append(self.run_parser.get_error_string())
         return
 
     def _load_generators(self):