src/Introspection/InputValueType.php
public function resolveDefaultValue($value)
    {
        $resolvedValue = $value->getConfig()->getDefaultValue();
        return $resolvedValue === null ? $resolvedValue : str_replace('"', '', json_encode($resolvedValue));
    }
public function resolveDefaultValue($value)
    {
        $resolvedValue = $value->getConfig()->getDefaultValue();
        return $resolvedValue === null ? $resolvedValue : str_replace('"', '', json_encode($resolvedValue));
    }
@param AbstractSchema|Field $value

@return string|null

//todo implement value printer