diff --git a/graphs_trees/graph/graph.py b/graphs_trees/graph/graph.py
index 03f0a62..755b4bb 100644
--- a/graphs_trees/graph/graph.py
+++ b/graphs_trees/graph/graph.py
@@ -23,15 +23,17 @@ class Node:
         return self.key < other.key
 
     def add_neighbor(self, neighbor, weight=0):
-        if neighbor is None:
-            raise Exception('Invalid neighbor')
+        if neighbor is None or weight is None:
+            raise TypeError('neighbor or weight cannot be None')
         neighbor.incoming_edges += 1
         self.adj_weights[neighbor.key] = weight
         self.adj_nodes[neighbor.key] = neighbor
 
     def remove_neighbor(self, neighbor):
-        if neighbor is None or neighbor.key not in self.adj_nodes:
-            raise Exception('Invalid neighbor')
+        if neighbor is None:
+            raise TypeError('neighbor cannot be None')
+        if neighbor.key not in self.adj_nodes:
+            raise KeyError('neighbor not found')
         neighbor.incoming_edges -= 1
         del self.adj_weights[neighbor.key]
         del self.adj_nodes[neighbor.key]
@@ -44,7 +46,7 @@ class Graph:
 
     def add_node(self, key):
         if key is None:
-            raise Exception('Invalid key')
+            raise TypeError('key cannot be None')
         if key in self.nodes:
             return self.nodes[key]
         self.nodes[key] = Node(key)
@@ -60,9 +62,8 @@ class Graph:
         self.nodes[source_key].add_neighbor(self.nodes[dest_key],
                                             weight)
 
-    def add_undirected_edge(self, source_key, dest_key, weight=0):
-        if source_key is None or dest_key is None:
-            raise Exception('Invalid key')
-        self.add_edge(source_key, dest_key, weight)
-        self.nodes[dest_key].add_neighbor(self.nodes[source_key],
-                                          weight)
\ No newline at end of file
+    def add_undirected_edge(self, src_key, dst_key, weight=0):
+        if src_key is None or dst_key is None:
+            raise TypeError('key cannot be None')
+        self.add_edge(src_key, dst_key, weight)
+        self.add_edge(dst_key, src_key, weight)
\ No newline at end of file
diff --git a/graphs_trees/graph/graph_challenge.ipynb b/graphs_trees/graph/graph_challenge.ipynb
index 21c61f8..091ae49 100644
--- a/graphs_trees/graph/graph_challenge.ipynb
+++ b/graphs_trees/graph/graph_challenge.ipynb
@@ -38,12 +38,14 @@
     "    * Implement both\n",
     "* Do the edges have weights?\n",
     "    * Yes\n",
-    "* Can we assume the inputs are valid?\n",
+    "* Can the graph have cycles?\n",
     "    * Yes\n",
     "* If we try to add a node that already exists, do we just do nothing?\n",
     "    * Yes\n",
     "* If we try to delete a node that doesn't exist, do we just do nothing?\n",
     "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * Yes\n",
     "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
diff --git a/graphs_trees/graph/graph_solution.ipynb b/graphs_trees/graph/graph_solution.ipynb
index 7221c82..64ec832 100644
--- a/graphs_trees/graph/graph_solution.ipynb
+++ b/graphs_trees/graph/graph_solution.ipynb
@@ -37,10 +37,14 @@
     "    * Implement both\n",
     "* Do the edges have weights?\n",
     "    * Yes\n",
+    "* Can the graph have cycles?\n",
+    "    * Yes\n",
     "* If we try to add a node that already exists, do we just do nothing?\n",
     "    * Yes\n",
     "* If we try to delete a node that doesn't exist, do we just do nothing?\n",
     "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * Yes\n",
     "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
@@ -187,15 +191,17 @@
     "        return self.key < other.key\n",
     "\n",
     "    def add_neighbor(self, neighbor, weight=0):\n",
-    "        if neighbor is None:\n",
-    "            raise Exception('Invalid neighbor')\n",
+    "        if neighbor is None or weight is None:\n",
+    "            raise TypeError('neighbor or weight cannot be None')\n",
     "        neighbor.incoming_edges += 1\n",
     "        self.adj_weights[neighbor.key] = weight\n",
     "        self.adj_nodes[neighbor.key] = neighbor\n",
     "\n",
     "    def remove_neighbor(self, neighbor):\n",
-    "        if neighbor is None or neighbor.key not in self.adj_nodes:\n",
-    "            raise Exception('Invalid neighbor')\n",
+    "        if neighbor is None:\n",
+    "            raise TypeError('neighbor cannot be None')\n",
+    "        if neighbor.key not in self.adj_nodes:\n",
+    "            raise KeyError('neighbor not found')\n",
     "        neighbor.incoming_edges -= 1\n",
     "        del self.adj_weights[neighbor.key]\n",
     "        del self.adj_nodes[neighbor.key]\n",
@@ -208,7 +214,7 @@
     "\n",
     "    def add_node(self, key):\n",
     "        if key is None:\n",
-    "            raise Exception('Invalid key')\n",
+    "            raise TypeError('key cannot be None')\n",
     "        if key in self.nodes:\n",
     "            return self.nodes[key]\n",
     "        self.nodes[key] = Node(key)\n",
@@ -224,12 +230,11 @@
     "        self.nodes[source_key].add_neighbor(self.nodes[dest_key],\n",
     "                                            weight)\n",
     "\n",
-    "    def add_undirected_edge(self, source_key, dest_key, weight=0):\n",
-    "        if source_key is None or dest_key is None:\n",
-    "            raise Exception('Invalid key')\n",
-    "        self.add_edge(source_key, dest_key, weight)\n",
-    "        self.nodes[dest_key].add_neighbor(self.nodes[source_key],\n",
-    "                                          weight)"
+    "    def add_undirected_edge(self, src_key, dst_key, weight=0):\n",
+    "        if src_key is None or dst_key is None:\n",
+    "            raise TypeError('key cannot be None')\n",
+    "        self.add_edge(src_key, dst_key, weight)\n",
+    "        self.add_edge(dst_key, src_key, weight)"
    ]
   },
   {