r – The use of date in biwavelet generate error of check.datum()

I am using CWT through biwavelet package to generate results of the Continuous Wavelet Spectrum of a time series. I have 245 observations of the time series. I used the below code and it correctly produced the graph.

EXR = data.frame(1:245,EX)
plot(wt(EXR), main="Continuous Wavelet Spectrum:C")

However, on the x-axis I get numbers from 0 to 240. I want to mention the date on the x-axis. Therefore, I made changes int the code as follows:

class(date)

(1) "Date"

EXR = data.frame(date,EX)
plot(wt(EXR), main="Continuous Wavelet Spectrum:C")

The following error is produced after the new code.

Error in check.datum(d) : The step size must be constant (see approx function to interpolate)

How I can rectify this error.