stan_surv doesn't interpret correctly NAs with type="interval2" survival data

Summary:

stan_surv doesn't interpret correcty the convention of having NAs instead of infinite values with type = "interval2" survival data.

Description:

As per ?Surv, when type = "interval2" is specified, "Infinite values can be represented either by actual infinity (Inf) or NA. The second form has proven to be the more useful one."

However, stan_surv seem to interpret correctly only the first form (infinite values).

From the reproducible example below.
First form (infinite values):

stan_surv
 baseline hazard: M-splines on hazard scale
 formula:         Surv(l, u, type = "interval2") ~ grp
 observations:    144
 events:          0 (0%)
 left censored:   62 (43.1%)
 right censored:  82 (56.9%)
 delayed entry:   no

Second form (NAs):

stan_surv
 baseline hazard: M-splines on hazard scale
 formula:         Surv(l, u, type = "interval2") ~ grp
 observations:    82
 events:          0 (0%)
 right censored:  82 (100%)
 delayed entry:   no

Reproducible Steps:

library(rstanarm)
library(tidyverse)

stan_surv(Surv(l, u, type = "interval2") ~ grp, 
          data = mice, chains = 1, refresh = 0, iter = 600)

mice2 <- 
  mice %>% 
  mutate(l = replace(l, is.infinite(l), NA_real_),
         u = replace(u, is.infinite(l), NA_real_))

stan_surv(Surv(l, u, type = "interval2") ~ grp, 
                        data = mice2, chains = 1, refresh = 0, iter = 600)

RStanARM Version:

2.21.2

R Version:

3.6.3

Operating System:

OS X 10.14.6

Start with the reproducible stan_surv examples in this issue, comparing interval2 data represented with Inf against the equivalent NA values. Trace how stan_surv preprocesses Surv(l, u, type = "interval2") inputs. Done means both representations produce the same observation, left-censoring, and right-censoring counts; add a regression test if the existing test structure is located.