Error with mediation package in R when using a categorical mediator

Question

I am trying to run a mediation model using the mediation pacakge. However, when I run the below code I get an error (see below). I think this may have something to do with the mediator being an ordered categorical variable. Has anyone found a solution to this issue?

Error in glm.fit(x = c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  : 
  NA/NaN/Inf in 'y'
In addition: Warning messages:
1: In Ops.factor(y, mu) : ‘-’ not meaningful for factors
2: In Ops.factor(eta, offset) : ‘-’ not meaningful for factors
3: In Ops.factor(y, mu) : ‘-’ not meaningful for factors
                      

The code to reproduce this error is as follows

# get packages
library(mediation)
library(mice)
library(tidyverse)

# create multipkle imputed dataset
boys2 <- mice(boys, 4) %>% 
  complete("all")


## To use mediations, must make list of multiple datasets. Then,
## must also repeat the treatment assignment list as many times
## as you have data sets.

# set up dataset for mediation analyses
datasets <- list(D1 = boys2$`1`, 
                 D2 = boys2$`2`,
                 D3 = boys2$`3`,
                 D4 = boys2$`4`,
                 D5 = boys2$`5`) # list of multiply imputed data sets

# run the mediation model
olsols <- mediations(datasets, 
                     treatment =  c("phb", "phb", "phb", "phb", "phb") , 
                     mediators = c("reg"), 
                     outcome =  c("bmi"), 
                     covariates =  c("wgt + age"),
                     families=c("gaussian","gaussian"), interaction=FALSE,
                     conf.level=.90, sims=1000)

output <- amelidiate(olsols)

# output
summary(output)