# Is the Mann Kendall test still effective with a lot of NA?

Recently I need to test the trend of a time series from 1665 to 1991 and I am going to use the MannKendall test in R. However, I finally found that I only have 210 values instead of the whole 256. There are 46 NAs in my data.

And I just used the MannKendall() in Kendall package in R and got that the P of my data is not significant. I don't know whether with so many NAs I could still just use the MannKendall() to test my data's trend.

Is it still effective? or do I need to transfer my NAs to other values?