diff --git a/src/mpIterator.py b/src/mpIterator.py
index 9f0863f..e922225 100755
--- a/src/mpIterator.py
+++ b/src/mpIterator.py
@@ -74,8 +74,8 @@ for test_name in [name for name in os.listdir(tests_dir) if os.path.isdir(os.pat
 	with open(validation_file, 'r') as f:
 		validations = load(f)
 	if validations!=None:
-		if "checkers" in validations:
-			for k in validations["checkers"].keys():
+		if "checkers" in validations and validations["checkers"]!=None:
+			for k in validations["checkers"]:
 				# Identify checker class
 				name = k.title().replace("_","")+"Checker"
 				klass= globals()[name]
@@ -85,7 +85,7 @@ for test_name in [name for name in os.listdir(tests_dir) if os.path.isdir(os.pat
 					print checker.logs
 				else:
 					print checker.logs
-		if "aggregators" in validations:
+		if "aggregators" in validations and validations["aggregators"]!=None:
 			for k in validations["aggregators"]:
 				# Identify checker class
 				name = k.title().replace("_","")+"Aggregator"