Problem Using :substitute to Replace Empty Fields in Tab Delimited File

Hi,

In a tab delimited data file I want to replace empty fields with \N. I wasn't getting the result I expected and began working with a simple test file that looked as follows with set list:

^I^I^I^I^I$
^I^I^I^I$
^I^I^I$
^I^I$
^I$
$

The desired result would be:

\N^I\N^I\N^I\N^I\N^I\N$
\N^I\N^I\N^I\N^I\N$
\N^I\N^I\N^I\N$
\N^I\N^I\N$
\N^I\N$
\N$

What I started with, and what seemed the most obvious way to do it, doesn't work, leaving the final field of multi-field lines unfilled:

%s/\(^\|\t\)\@<=\(\t\|$\)\@=/\\N/g

The following works, the only difference being the match on end-of-line instead of end-of-line at end of pattern with zero width:

%s/\(^\|\t\)\@<=\(\t\|\n\)\@=/\\N/g

Using zs and ze instead of @<= and @=, the following did not work, strangely leaving the second field of multi-field lines unfilled:

%s/\(^\|\t\)\zs\ze\(\t\|$\)/\\N/g

Both of the commands above that failed achieve the desired result if executed repeatedly until the command returns E486: Pattern not found: ….

Vim is v7.3.429 as packaged for the Lubuntu 12.04 repositories.

Am I misunderstanding something or is Vim not handling this correctly?

Thanks for reading along and any help you may offer.

John Slattery

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