downgrade to kirby v3

kirby/src/Form/Mixin/EmptyState.php

@@ -4,14 +4,14 @@ namespace Kirby\Form\Mixin;
 
 trait EmptyState
 {
-	protected string|null $empty;
+	protected $empty;
 
-	protected function setEmpty(string|array|null $empty = null): void
+	protected function setEmpty($empty = null)
 	{
 		$this->empty = $this->i18n($empty);
 	}
 
-	public function empty(): string|null
+	public function empty(): ?string
 	{
 		return $this->stringTemplate($this->empty);
 	}

kirby/src/Form/Mixin/Max.php

@@ -4,9 +4,9 @@ namespace Kirby\Form\Mixin;
 
 trait Max
 {
-	protected int|null $max;
+	protected $max;
 
-	public function max(): int|null
+	public function max(): ?int
 	{
 		return $this->max;
 	}

kirby/src/Form/Mixin/Min.php

@@ -4,9 +4,9 @@ namespace Kirby\Form\Mixin;
 
 trait Min
 {
-	protected int|null $min;
+	protected $min;
 
-	public function min(): int|null
+	public function min(): ?int
 	{
 		return $this->min;
 	}