src/Collection.php
public function toJson($prettyPrint = false)
    {
        $options = 0;
        if ($prettyPrint) {
            $options += JSON_PRETTY_PRINT;
        }
        return json_encode($this->items, $options);
    }
public function toJson($prettyPrint = false)
    {
        $options = 0;
        if ($prettyPrint) {
            $options += JSON_PRETTY_PRINT;
        }
        return json_encode($this->items, $options);
    }
To json.

@param boolean $prettyPrint Default false.
@return string