diff --git a/jellyfish/_jellyfish.py b/jellyfish/_jellyfish.py
index <HASH>..<HASH> 100644
--- a/jellyfish/_jellyfish.py
+++ b/jellyfish/_jellyfish.py
@@ -220,11 +220,11 @@ def hamming_distance(s1, s2):
 
 
 def nysiis(s):
-    _check_type(s)
-
     if not s:
         return ''
 
+    _check_type(s)
+
     s = s.upper()
     key = []
NoneType has to be checked first

This needs a test