fix(support): support calling first and last on empty ArrayHelper (#691)

Author: innocenzi

src/Tempest/Support/src/ArrayHelper.php

@@ -384,6 +384,10 @@ public function equals(array|self $other): bool
      */
     public function first(?Closure $filter = null): mixed
     {
+        if ($this->array === []) {
+            return null;
+        }
+
         if ($filter === null) {
             return $this->array[array_key_first($this->array)];
         }
@@ -405,6 +409,10 @@ public function first(?Closure $filter = null): mixed
      */
     public function last(?Closure $filter = null): mixed
     {
+        if ($this->array === []) {
+            return null;
+        }
+
         if ($filter === null) {
             return $this->array[array_key_last($this->array)];
         }

src/Tempest/Support/tests/ArrayHelperTest.php

@@ -178,12 +178,14 @@ public function test_unshift(): void
 
     public function test_last(): void
     {
+        $this->assertSame(null, arr()->last());
         $this->assertSame('c', arr(['a', 'b', 'c'])->last());
     }
 
     public function test_first(): void
     {
         $this->assertSame('a', arr(['a', 'b', 'c'])->first());
+        $this->assertSame(null, arr()->first());
     }
 
     public function test_is_empty(): void