Issue in generating plot

[Bioinfo9]

Hi ..
I am trying to create plot for chip data using non standard ref. All commands work fine except for :

track_plot(summary_list = t)

It shows:
Error in round(plot_height, digits = 2) :
non-numeric argument to mathematical function

This is my set of commands:
library("trackplot")

Sys.setenv(PATH = paste("/data/ngs/programs/bwtool/bwtool-1.0-gamma/bwtool", Sys.getenv("PATH"), sep = ":"))

bigWigs = c("n.bw")

bigWigs = read_coldata(bws = bigWigs, build = GCA_000146045.2_R64_genomic_mod.fna")

oct4_loci = "chrBK006945.2:1-1078177"

t = track_extract(colData = bigWigs, loci = oct4_loci, query_ucsc = FALSE, gtf="genomic_mod.gtf")

track_plot(summary_list = t)
Thank you.