Issue when output = "covariate" for diagnostic.plot()

[XiaoruiZhu]

data("ANES2016")
# Partial association between "PreVote.num" and "PID" after adjusting "income.num", "age", "edu.year"
# "PAsso" function: Only need input responses, adjustments, data
PAsso_1 <- PAsso(responses = c("PreVote.num", "PID"),
adjustments = c("income.num", "age", "edu.year"),
data = ANES2016,
uni.model = "probit",
method = c("kendall"))
diagnostic.plot(object = PAsso_1, output = "covariate", x_name = "income.num", model_id = 2)

Error in assign(x = x_name, object$data[, x_name]) : invalid first argument