Added a validator that checks, if a values is empty, if another one is set.

app/CustomValidator.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace App;
+
+use Illuminate\Validation\Validator;
+
+class CustomValidator extends Validator
+{
+    public function validateEmpty($attribute, $value)
+    {
+        return !$this->validateRequired($attribute, $value);
+    }
+
+    public function validateEmptyIf($attribute, $value, $parameters)
+    {
+        $key = $parameters[0];
+
+        if ($this->validateRequired($key, $this->getValue($key))) {
+            return $this->validateEmpty($attribute, $value);
+        }
+
+        return true;
+    }
+}