Error in xy coords x y xlabel ylabel log x and y lengths differ

Question

Hi, so I am a new Rstudio user and I am trying to make a line graph with multiple lines. Then, I am getting an error message that says "Error in xy.coords(x, y, xlabel, ylabel, log) : 'x' and 'y' lengths differ".

The code is

plot(a$week.no,a$no.case,type='p',ylim=c(0,64),col='black',pch=19,cex.axis=1.2,
     cex=1.2, cex.lab=1.2,xlab="week.no",ylab="number new case")

and I already ran

> length(a$week.no)
[1] 0
> length(a$no.case)
[1] 64

Please, I want this help