`filter(dd, ...)` throws bad error when `names(dd)` contains `NA`

[jaganmn]

filter(dd, ...) complains about non-existent zero-length variable names when names(dd) contains NA:

library(dplyr)
dd <- data.frame(1:10, rnorm(10), letters[1:10])
names(dd) <- c("a", "b", NA)
filter(dd, b > 0)
## Error in initialize(...) : attempt to use zero-length variable name

Debugging details here: https://stackoverflow.com/a/75553014/12685768