Problems in summary(ppool_syn)

[Seveyrin]

Hello!
I successfully got the results after using multisynth as:

ppool_syn
Call:
multisynth(form = expense ~ received_treated, unit = firm_id,
time = year, data = data, n_leads = 5, n_lags = 5)
Average ATT Estimate: 7.705

But when I run the later code of summary, it reports error as:

ppool_syn_summ <- summary(ppool_syn)
Error:
! Names repair functions can't return NA values.

I have no problem running the example of Paglayan (2018). This error happened when I used it in my own data, so I'm not sure if there's anything I missed...Once the number of treated units (firms) in my data is larger than 240, it will report such error.

Thanks for any help in advance!