csv::split handles a quoted, null field incorrectly if
the field is neither the first nor the last field in a
line/record:

% info tclversion
8.3
% info patch
8.3.3
% package require csv
0.2
% ::csv::split {1 2 "" ""} { }
1 2 {"} {}
% ::csv::split {"" ""} { }
{} {}
% ::csv::split {"" "" ""} { }
{} {"} {}

A change to the character map seems to fix the problem:

% proc ::csv::split {line {sepChar ,}} {
    regsub -all -- {(^\"|\"$)} $line \0 line
    set line [string map [list \
    $sepChar\"\"\" $sepChar\0\" \
    \"\"\"$sepChar \"\0$sepChar \
    \"\"$sepChar $sepChar \
    \"\"           \" \
    \"             \0 \
    ] $line]
    set end 0
    while {[regexp -indices -start $end --
{(\0)[^\0]*(\0)} $line \
    -> start end]} {
set start [lindex $start 0]
set end   [lindex $end 0]
set range [string range $line $start $end]
if {[string first $sepChar $range] >= 0} {
    set line [string replace $line $start $end \
    [string map [list $sepChar \1] $range]]
}
incr end
    }
    set line [string map [list $sepChar \0 \1 $sepChar
\0 {} ] $line]
    return [::split $line \0]
}
% ::csv::split {"" "" "" "" "" ""} { }
{} {} {} {} {} {}

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Patch applied to head and committed.

File Added - 25748: 565051.diff

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Here is a patch for the true problem. Contains an extended 
testsuite.

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There is a bug in split parsing, but it is not in the handling of 
inner fields. It is the outer fields, i.e. first and last which are 
off, i.e. wrongly handled.

The string {"" "" ""} parsed with separator character <space> 
does not contain three empty fields. It contains 3 fields each 
of which contains a single ". See the definition of the CSV 
format. This might be even more clear when parsing {"","",""} 
using the comma as separator character. An empty field is 
specified by two adjacent separator characters without any 
intervening other characters. In the case of <space> this 
means a space following a space, or a space at beginning 
and/or end of the string.

File Added - 24471: csv.tcl

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A revised version of cvs.tcl is attached.  Still csv package
version number 0.2.