src/Reflection/ReflectionFunctionAbstract.php
public function addParameter(string $parameterName) : void
    {
        $this->node->params[] = new ParamNode(new Node\Expr\Variable($parameterName));
    }
public function addParameter(string $parameterName) : void
    {
        $this->node->params[] = new ParamNode(new Node\Expr\Variable($parameterName));
    }
Add a new parameter to the method/function.