iebaltab: onerow option generates error if non-varying variable is included even when there is no missingness

[jmseiden]

When using the onerow option, iebaltab generates the error "Option onerow may only be used if the number of observations with non-missing values are the same in all groups across all balance variables." even when the number of observations are non-missing for all variables if a non-varying variable is included.

Here is a reproducible example.

clear all
sysuse auto

gen constant_var = 1 // Create a variable that is the same for all observations

sum foreign weight length constant_var //All variables have the same number of observations

iebaltab weight length, groupvar(foreign) onerow //works fine

iebaltab weight length constant_var , groupvar(foreign) onerow //generates an error

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