Can't count the null values of a dataframe in R

General
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2

NULL and NA are distinct. NULL means "not defined" and NA means "missing". The screenshot and the output of colSums() show that some NAs are present.

sum(is.na(your_data))

will return the total number in the data frame.

colSums(is.na(your_data))

gives the count of NA by column, and

rowSums(your_data)

shows the rows containing NA.

If

isn't working, we'd need to look at a representative data set. See the FAQ: How to do a minimal reproducible example reprex for beginners.