add nullable to checkbox

src/Form/Element/Checkbox.php

@@ -12,7 +12,8 @@
 
 class Checkbox extends Element
 {
-    protected $options = [];
+    protected $options  = [];
+    protected $nullable = false;
 
     public function view()
     {
@@ -25,12 +26,28 @@ public function view()
             'checked'     => $this->value,
             'options'     => $this->options,
             'class'       => $this->class,
-            'attributes'  => $this->attributes
+            'attributes'  => $this->attributes,
+            'nullable'    => $this->nullable,
         ]);
     }
 
     public function value()
     {
-        return $this->value ? 1 : 0;
+        $value = null;
+
+        if ($this->value) {
+            $value = 1;
+        } elseif (!$this->nullable) {
+            $value = 0;
+        }
+
+        return $value;
+    }
+
+    public function nullable($nullable = true)
+    {
+        $this->nullable = $nullable;
+
+        return $this;
     }
 }

src/resources/views/default/element/checkbox.blade.php

@@ -1,6 +1,8 @@
 <div class="form__element form__element_type_checkbox @if($error) form__element_error @endif {{$class}}">
     <label class="form__label">
-        <input type="hidden" value="0" name="{{ $elementName }}">
+        @if (!$nullable)
+            <input type="hidden" value="0" name="{{ $elementName }}">
+        @endif
         <input @foreach($attributes as $attributeName => $attributeValue) {{ $attributeName }}="{{ $attributeValue }}" @endforeach type="checkbox" value="1" @if($checked) checked="checked" @endif name="{{ $elementName }}"> <span>{{ $label  }}</span>
         <div class="form__help">{{ $help }}</div>
         <div class="form__feedback">{{ $error }}</div>