error when `new` is missing and `old` contains `NA`
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  namesDict <- invDict(dict.TWACNames)

  # all the column names to replace
  namesDict[names(mainDT)]

  # have a value be missing
  names(namesDict)[[2]] <- "I_AM_MISSING"

  # note the NA
  namesDict[names(mainDT)]

  setnames(mainDT,  namesDict[names(mainDT)])

  # now cannot print mainDT
  mainDT
  Error in if (!all(names(allargs[[i]]) == nm)) if (missing(use.names)) warning("Argument ",  : 
    missing value where TRUE/FALSE needed

  # this is the same error we get if we try to use `setNames` (from `base`)
  setNames(mainDT, namesDict[names(mainDT)])
  Error in if (!all(names(allargs[[i]]) == nm)) if (missing(use.names)) warning("Argument ",  : 
    missing value where TRUE/FALSE needed