SCtools can't use plot_placebos

[uohenSS]

I am trying to use Synth and SCtools package in R. But the plot_placebos command always reports "Error in plot_placebos(placebos) : .meta column has been removed. .meta column needs to be included for generte_control() to work." Does anyone meet this problem before? Thank you!

The code is

library(tidyverse)
library(haven)
library(Synth)
library(devtools)
if(!require(SCtools)) devtools::install_github("bcastanho/SCtools")
library(SCtools)

read_data <- function(df)
{
  full_path <- paste("https://raw.github.com/scunning1975/mixtape/master/", 
                     df, sep = "")
  df <- read_dta(full_path)
  return(df)
}

texas <- read_data("texas.dta") %>%
  as.data.frame(.)

dataprep_out <- dataprep(
  foo = texas,
  predictors = c("poverty", "income"),
  predictors.op = "mean",
  time.predictors.prior = 1985:1993,
  special.predictors = list(
    list("bmprison", c(1988, 1990:1992), "mean"),
    list("alcohol", 1990, "mean"),
    list("aidscapita", 1990:1991, "mean"),
    list("black", 1990:1992, "mean"),
    list("perc1519", 1990, "mean")),
  dependent = "bmprison",
  unit.variable = "statefip",
  unit.names.variable = "state",
  time.variable = "year",
  treatment.identifier = 48,
  controls.identifier = c(1,2,4:6,8:13,15:42,44:47,49:51,53:56),
  time.optimize.ssr = 1985:1993,
  time.plot = 1985:2000
)

synth_out <- synth(data.prep.obj = dataprep_out)

placebos <- generate.placebos(dataprep_out, synth_out, Sigf.ipop = 3)

plot_placebos(placebos)