src/Reflection/ReflectionFunctionAbstract.php
public function getParameter(string $parameterName) : ?ReflectionParameter
    {
        foreach ($this->getParameters() as $parameter) {
            if ($parameter->getName() === $parameterName) {
                return $parameter;
            }
        }

        return null;
    }
public function getParameter(string $parameterName) : ?ReflectionParameter
    {
        foreach ($this->getParameters() as $parameter) {
            if ($parameter->getName() === $parameterName) {
                return $parameter;
            }
        }

        return null;
    }
Get a single parameter by name. Returns null if parameter not found for
the function.