function that pre-processes regression objects of type lm, fixest and feols
preprocess2(object, cluster, fe, param, bootcluster, na_omit)
An object of class lm, fixest or felm
A vector with the names of the clusters
A character scalar - fixed effect to be projected out, or NULL
The univariate coefficients for which a hypothesis is to be tested
The bootstrap sampling cluster.
Logical. If TRUE, boottest()
omits rows with missing variables that are added to the model via the cluster
argument in boottest()
List containing preprocessed data for boottest estimation