initialize client field to NULL in wm_treenode_new

src/client.c

@@ -168,9 +168,9 @@ void wm_client_focus(Wm *wm, Client *c)
     Client *old_focused_client = wm->focused_client;
     if (!old_focused_client)
         old_focused_client = wm_client_get_focused(wm);
-    assert(old_focused_client);
 
-    old_focused_client->focused = false;
+    if (old_focused_client)
+        old_focused_client->focused = false;
 
     XSetInputFocus(wm->display, c->window, RevertToPointerRoot, CurrentTime);
     wm_client_set_atom(wm, c, "_NET_ACTIVE_WINDOW", (unsigned char*) &c->window,
@@ -376,7 +376,9 @@ Client* wm_client_get_focused(Wm *wm)
 
     Workspace *ws = &wm->smon->workspaces[wm->smon->selws];
     TreeNode *node = wm_treenode_ptr_find_focused_client_node(&ws->tree);
-    assert(node);
+
+    if (!node)
+        return NULL;
 
     return node->client;
 }

src/util.c

@@ -16,6 +16,7 @@ TreeNode wm_treenode_new(NodeType type, TreeNode *parent)
 
     node_id++;
     node.id = node_id;
+    node.client = NULL;
 
     return node;
 }