st: mlogit with empty cell

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Hi,
I consider the follwoing model ,

xi: mlogit y   i.x1   i.x2    x3,    baseoutcome(1) rrr

with    y    is a discrete varaible with 4 categories,
x1 dichotomious ,
x2  discrete varaible with 4 categories
and x3 is continnuous

the cross tab of y and x2 gives one empty cell

How I can fit the model by taking into account the "empty cell"?

Thanks a lot for any help

Sami

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