diff --git a/openmc/checkvalue.py b/openmc/checkvalue.py
index 32d14c6f8f..a59b38a630 100644
--- a/openmc/checkvalue.py
+++ b/openmc/checkvalue.py
@@ -19,7 +19,7 @@ def check_type(name, value, expected_type, expected_iter_type=None, *, none_ok=F
     expected_iter_type : type or Iterable of type or None, optional
         Expected type of each element in value, assuming it is iterable. If
         None, no check will be performed.
-    none_ok : bool
+    none_ok : bool, optional
         Whether None is allowed as a value
 
     """
diff --git a/openmc/material.py b/openmc/material.py
index 0e1ae8df7b..3babdf6435 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -794,10 +794,10 @@ class Material(IDManagerMixin):
         xml_element = ET.Element("nuclide")
         xml_element.set("name", nuclide[0])
 
-        if nuclide[2] == 'ao':
-            xml_element.set("ao", str(nuclide[1]))
+        if nuclide.percent_type == 'ao':
+            xml_element.set("ao", str(nuclide.percent))
         else:
-            xml_element.set("wo", str(nuclide[1]))
+            xml_element.set("wo", str(nuclide.percent))
 
         return xml_element
 
diff --git a/openmc/tallies.py b/openmc/tallies.py
index e27b750a65..11f2fb0676 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -1097,7 +1097,7 @@ class Tally(IDManagerMixin):
             return np.arange(self.num_nuclides)
 
         # Determine the score indices from any of the requested scores
-        nuclide_indices = np.zeros(len(nuclides), dtype=int)
+        nuclide_indices = np.zeros_like(nuclides, dtype=int)
         for i, nuclide in enumerate(nuclides):
             nuclide_indices[i] = self.get_nuclide_index(nuclide)
         return nuclide_indices