The issue #20681 describe the error of delete() function
removing the elements from the origin array/hash/string.
This issue affected other delete functions. Because
ruby delete and delete_if functions make destructive
changes to the origin array/hash.
The delete_undef_values removed elements from the
origin array/hash and this is not the desired behaviour.
To solve this, we should dup or clone the array/hash
before using the delete or delete_if ruby functions.
We should also check if args[0] is not nil before using
dup, since dup on nil raises exception.
This fix the problem and add unit tests, so we could
enforce this behaviour and prevent regressions.
