public void FunctionExpressionHelpersNeedsExpression()
{
FunctionExpression expression = null;
Expect.Throw <ArgumentNullException>(() => expression.Parameters());
Expect.Throw <ArgumentNullException>(() => expression.Parameters(new List <IdentifierExpression>()));
Expect.Throw <ArgumentNullException>(() => expression.Do());
Expect.Throw <ArgumentNullException>(() => expression.Do(new List <Statement>()));
}