Pinq\Queries\Builders\ExpressionInterpreter::getOptionalFunctionAt PHP Method

    protected final function getOptionalFunctionAt($name, $index, O\MethodCallExpression $expression)
    {
        $argument = $this->getOptionalArgumentAt($index, $expression);
        if ($argument === null || $argument instanceof O\ValueExpression && $argument->getValue() === null) {
            return null;
        }
        return $this->getFunction("{$name}-{$index}", $argument);
    }