diff --git a/datasets/raise/utils.py b/datasets/raise/utils.py
index 258c80a..1ce8916 100644
--- a/datasets/raise/utils.py
+++ b/datasets/raise/utils.py
@@ -31,5 +31,8 @@ class iterativeMean:
     numberOfElementsInMean = 0
 
     def add(self, element):
-        self.mean = ((self.mean * self.numberOfElementsInMean) + element) / (self.numberOfElementsInMean + 1)
-        self.numberOfElementsInMean += 1
\ No newline at end of file
+        if self.mean is None:
+            self.mean = element
+        else:
+            self.mean = ((self.mean * self.numberOfElementsInMean) + element) / (self.numberOfElementsInMean + 1)
+        self.numberOfElementsInMean += 1