Ggbio Autoplot Error, Negative Length Vectors Are Not Allowed

Question

[paulr]

Dear all, So I'm trying to use autoplot from the Bioconductor ggbio package. For some reason, the following data and code causes an odd error.

library(ggbio)
data(hg19IdeogramCyto, package = "biovizBase")
require(TxDb.Hsapiens.UCSC.hg19.knownGene)
txdb <- TxDb.Hsapiens.UCSC.hg19.knownGene
sample.data <- data.frame(chromosome='chr7', begin= 6018314, end= 6018316)
actual.var <- GRanges(seqnames=sample.data$chromosome, IRanges(start=sample.data$begin, end=sample.data$end))
p.2 <- autoplot(txdb, which = actual.var, color='blue', names.expr = "gene_id:::tx_name")

And here's the output and subsequent error

Aggregating TranscriptDb...
Parsing exons...
Parsing cds...
Parsing transcripts...
Aggregating... 
Done
Constructing graphics...
Error in approx(c(x.s, x.e), rep(0, 2), n = N) : 
  negative length vectors are not allowed

Does GRanges require at least two coordinates? I just want to indicate where a small variant occurs.

Thanks in advance!