Examples for call_modify use NULL in place of zap()

[nicholasdavies]

There are three places in the Examples in the documentation for call_modify() that appear to erroneously use NULL to remove an argument instead of zap():

# Supply a list of new arguments with `!!!`
newargs <- list(na.rm = NULL, trim = 0.1)
call <- call_modify(call, !!!newargs)
call

# ...

# By default, arguments with the same name are kept. This has
# subtle implications, for instance you can move an argument to
# last position by removing it and remapping it:
call <- quote(foo(bar = , baz))
call_modify(call, bar = NULL, bar = missing_arg())

# You can also choose to keep only the first or last homonym
# arguments:
args <-  list(bar = NULL, bar = missing_arg())
call_modify(call, !!!args, .homonyms = "first")
call_modify(call, !!!args, .homonyms = "last")