Remove redundant check

src/Illuminate/Validation/Concerns/ValidatesAttributes.php

@@ -1516,7 +1516,7 @@ protected function prepareValuesAndOther($parameters)
             $values = $this->convertValuesToBoolean($values);
         }
 
-        if ($this->shouldConvertToNull($parameters[0]) || is_null($other)) {
+        if (is_null($other)) {
             $values = $this->convertValuesToNull($values);
         }
 
@@ -1534,17 +1534,6 @@ protected function shouldConvertToBoolean($parameter)
         return in_array('boolean', Arr::get($this->rules, $parameter, []));
     }
 
-    /**
-     * Check if parameter should be converted to null.
-     *
-     * @param  string  $parameter
-     * @return bool
-     */
-    protected function shouldConvertToNull($parameter)
-    {
-        return in_array('nullable', Arr::get($this->rules, $parameter, []));
-    }
-
     /**
      * Convert the given values to boolean if they are string "true" / "false".
      *
@@ -1573,11 +1562,7 @@ protected function convertValuesToBoolean($values)
     protected function convertValuesToNull($values)
     {
         return array_map(function ($value) {
-            if ($value === 'null') {
-                return null;
-            }
-
-            return $value;
+            return Str::lower($value) === 'null' ? null : $value;
         }, $values);
     }