Hi ravi,
I am not sure if you have already found solutions to your problem.
We used to get similar issue, when we used to convert an XML to a recordlist. If XML provided only one instance of data, it used to become a record in place of a recordlist at the time of using pub.web:documentToRecord. (I use webMethods 4.6). We solved it by using recordName parameter (it was always there, we missed it and someone on wmuser helped to remind)
If you ware copying data from one recordlist to another recordlist, and you wish to copy every segment, then you would not need to give any index. The cause of you getting null should be something else.
#webMethods#Flow-and-Java-services#Integration-Server-and-ESB