r - Error: invalid font type when knitting plot output to PDF

Question

When I tried to knit the below chunk to PDF, it raised Error in grid.Call.graphics(C_text, as.graphicsAnnot(x$label), x$x, x$y, : invalid font type. I don't know why it causes such an error as when I executed it in normal mode, it worked fine. Any help will be appreciated.

data <- data.frame(
  day = as.Date("2017-06-14") - 0:364,
  value = runif(365) + seq(-140, 224)^2 / 10000
)

# Most basic bubble plot
p <- ggplot(data, aes(x=day, y=value)) +
  geom_line( color="steelblue") + 
  geom_point() +
  xlab("") +
  theme_ipsum() +
  theme(axis.text.x=element_text(angle=60, hjust=1)) +
  scale_x_date(limit=c(as.Date("2017-01-01"),as.Date("2017-02-11"))) +
  ylim(0,1.5)

question from:https://stackoverflow.com/questions/65546071/error-invalid-font-type-when-knitting-plot-output-to-pdf

Answer 1

Waitting for answers