Object could not be converted to string

What is the problem?

Error: Object of class Xaoc\MainClass could not be converted to string
File: /src/pocketmine/command/Command
Line: 85
Type: E_RECOVERABLE_ERROR

Code:
[76] * @param string $name
[77] * @param string $description
[78] * @param string $usageMessage
[79] * @param string[] $aliases
[80] */
[81] public function __construct($name, $description = "", $usageMessage = null, array $aliases = []){
[82] $this->commandData = self::generateDefaultData();
[83] $this->name = $this->nextLabel = $this->label = $name;
[84] $this->setDescription($description);
[85] $this->usageMessage = $usageMessage === null ? "/" . $name : $usageMessage;
[86] $this->setAliases($aliases);
[87] $this->timings = new TimingsHandler("** Command: " . $name);
[88] }
[89]
[90] /**
[91] * Returns an \stdClass containing command data
[92] *
[93] * @return \stdClass
[94] */
[95] public function getDefaultCommandData() : \stdClass{

 

you aren't constructing class with string or null but with MainClass

 

It's difficult for me