Add is_null method to ARD

pyard/ard.py

@@ -529,6 +529,15 @@ def is_shortnull(self, allele):
         """
         return allele in self.shortnulls and self._config["reduce_shortnull"]
 
+    def is_null(self, allele):
+        """
+        Check if allele is a null allele.
+
+        @param allele: Allele to check for null
+        @return: boolean indicating whether allele is null or not
+        """
+        return allele.endswith("N") and not self.is_mac(allele)
+
     def is_exp_allele(self, allele):
         """
         Test if allele is valid as a shortening (WHO rules)

tests/test_pyard.py

@@ -186,3 +186,22 @@ def test_cache_info(self):
             another_ard._redux_allele.cache_info().maxsize, higher_cache_size
         )
         self.assertEqual(another_ard.redux.cache_info().maxsize, higher_cache_size)
+
+    def test_is_null(self):
+        # a null allele
+        allele = "A*01:01N"
+        self.assertTrue(self.ard.is_null(allele), msg="A Null Allele")
+        # not null allele
+        allele = "A*01:01"
+        self.assertFalse(self.ard.is_null(allele), msg="not null allele")
+        # MACs ending with N shouldn't be called as Nulls
+        allele = "A*01:MN"
+        self.assertFalse(
+            self.ard.is_null(allele),
+            msg="MACs ending with N shouldn't be called as Nulls",
+        )
+        # MACs shouldn't be called as Nulls
+        allele = "A*01:AB"
+        self.assertFalse(
+            self.ard.is_null(allele), msg="MACs shouldn't be called as Nulls"
+        )