diff --git a/src/Collect/Support/Collection.php b/src/Collect/Support/Collection.php
index 5ac3622..22e6a3d 100644
--- a/src/Collect/Support/Collection.php
+++ b/src/Collect/Support/Collection.php
@@ -376,7 +376,7 @@ public function except($keys)
      * @param (callable(TValue, TKey): bool)|null  $callback
      * @return static
      */
-    public function filter(callable $callback = null)
+    public function filter(?callable $callback = null)
     {
         if ($callback) {
             return new static(Arr::where($this->items, $callback));
@@ -394,7 +394,7 @@ public function filter(callable $callback = null)
      * @param  TFirstDefault|(\Closure(): TFirstDefault)  $default
      * @return TValue|TFirstDefault
      */
-    public function first(callable $callback = null, $default = null)
+    public function first(?callable $callback = null, $default = null)
     {
         return Arr::first($this->items, $callback, $default);
     }
@@ -741,7 +741,7 @@ public function keys()
      * @param  TLastDefault|(\Closure(): TLastDefault)  $default
      * @return TValue|TLastDefault
      */
-    public function last(callable $callback = null, $default = null)
+    public function last(?callable $callback = null, $default = null)
     {
         return Arr::last($this->items, $callback, $default);
     }