[R] Question from day2 beginner

[maxcheese]

Hello, I just started learning R and have a very basic question:

When I try ar model and extract residuals it returns Null.  Could someone
explain what's going on here?  Does that mean the model is null?  But it
seems residual has a length=# observation of the original series according
to the model summary.  I am learning it by myself and have no one to ask
here so please allow me to ask this very basic question...  Thank you very
much. 

> summary(ar(logrvar, aic=TRUE))

             Length Class  Mode     
order            1  -none- numeric  
ar              40  -none- numeric  
var.pred         1  -none- numeric  
x.mean           1  -none- numeric  
aic             44  -none- numeric  
n.used           1  -none- numeric  
order.max        1  -none- numeric  
partialacf      43  -none- numeric  
resid        20731  -none- numeric  
method           1  -none- character
series           1  -none- character
frequency        1  -none- numeric  
call             3  -none- call     
asy.var.coef  1600  -none- numeric  

> resid(ar(logrvar, aic=TRUE))
NULL
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