strange error in fitting parameters in ebm_j

cognitivemodels/tests/testthat/test_ebm_j.R

Line 147 in ce09e4e

    
           dt <- albrecht2019exp1[subj <= 42, list(fit_ebm_j = list(fit_ebm_j(dt = .SD))), by = list(subj)]

Executing this line for subjects 41 and 42 (subject ids start with 41) works perfectly. However, when I delete the "subj <= 42", I receive the following error already for the first participant for which the parameters are estimated:

Error in arr[, 1:na[s], s][] <- as.matrix(model.frame(formula(f, lhs = 0, :
replacement has length zero
error is located at: cm-class, line 276