Error with singleton observations

[pdeffebach]

This error occurs when there are singleton observations. It looks like GLFixedEffectModels.jl isn't keeping track of the number of observations well enough, and some indexing persists even after dropping singleton observations. Here is an MWE

julia> df = DataFrame(y = rand(100), x = rand(100), g = rand(1:10, 100));

julia> push!(df, (y = 0.5, x = 0.5, g = 11));

julia> m = nlreg(df, @formula(y ~ x + fe(g)), Poisson(), LogLink(), save = [:fe])
[ Info: 1 observations detected as singletons. Dropping them ...
ERROR: BoundsError: attempt to access 100×1 Matrix{Float64} at index [101-element BitVector, 1:1]
Stacktrace:

The bug only occurs when we have save = [:fe]. So it has to do with creating the augmentdf data frame

julia> m = nlreg(df, @formula(y ~ x + fe(g)), Poisson(), LogLink())
[ Info: 1 observations detected as singletons. Dropping them ...
             Generalized Linear Fixed Effect Model             
===============================================================
Distribution:        "Poisson"   Link:                "LogLink"
Number of obs:             100   Degrees of freedom:         11
Deviance:               19.013   Pseudo-R2:                 NaN
Pseudo-Adj. R2:            NaN   Iterations:                  5
Converged:                true   
===============================================================
      Estimate Std.Error   t value Pr(>|t|) Lower 95% Upper 95%
---------------------------------------------------------------
x    -0.343138  0.516953 -0.663771    0.509  -1.35635   0.67007
===============================================================