[Wrapper] explicitly return None for name/index finder functions

Author: maltanar

src/qonnx/core/modelwrapper.py

@@ -532,7 +532,7 @@ def get_non_finn_nodes(self):
         return list(filter(lambda x: not util.is_finn_op(x.domain), self.graph.node))
 
     def get_node_index(self, node):
-        """Returns current index of given node."""
+        """Returns current index of given node, or None if not found."""
         n_ind = 0
         try:
             for n in self.graph.node:
@@ -541,15 +541,17 @@ def get_node_index(self, node):
                 n_ind += 1
         except ValueError:
             return None
+        return None
 
     def get_node_from_name(self, node_name):
-        """Returns the node with the specified name."""
+        """Returns the node with the specified name, or None if not found."""
         try:
             for node in self.graph.node:
                 if node.name == node_name:
                     return node
         except ValueError:
             return None
+        return None
 
     def get_tensor_layout(self, tensor_name):
         """Returns the data layout annotation of tensor with given name.