Remove default setting from notify.handler

Author: ghostbuster91

doc/nvim-tree-lua.txt

@@ -440,7 +440,6 @@ applying configuration.
       },
       notify = {
         threshold = vim.log.levels.INFO,
-        handler = "default",
       },
       ui = {
         confirm = {
@@ -1226,10 +1225,10 @@ Configuration for notification.
     `DEBUG:`   not used.
 
     *nvim-tree.notify.handler*
-    Change the default notification handler, can be a string `"default"` or a function.
-    The default handler will check if the nvim-notify plugin is present on the
-    runtime path and use it, otherwise it will fallback to use `vim.notify`. 
-      Type: `string` | `function`, Default: `"default"`
+    Change the default notification handler. The default handler will
+    check if the nvim-notify plugin is present on the runtime path and
+    use it, otherwise it will fallback to use `vim.notify`. 
+      Type: `function` 
 
     The function will be called with following parameters:
 

lua/nvim-tree.lua

@@ -629,7 +629,6 @@ local DEFAULT_OPTS = { -- BEGIN_DEFAULT_OPTS
   },
   notify = {
     threshold = vim.log.levels.INFO,
-    handler = "default",
   },
   ui = {
     confirm = {
@@ -664,6 +663,7 @@ end
 
 local FIELD_SKIP_VALIDATE = {
   open_win_config = true,
+  handler = true,
 }
 
 local FIELD_OVERRIDE_TYPECHECK = {
@@ -675,7 +675,6 @@ local FIELD_OVERRIDE_TYPECHECK = {
   sort_by = { ["function"] = true, string = true },
   root_folder_label = { ["function"] = true, string = true },
   picker = { ["function"] = true, string = true },
-  handler = { ["function"] = true, string = true },
 }
 
 local function validate_options(conf)