Puzzlement : empty field vs. ,field() -m

[Jim Freeman]

In splitting out fields from req.cook, populated fields work well, but
detecting an unset field has me befuddled:

  acl COOK_META_MISSING  req.cook(cook2hdr),field(3,\#) ! -m found -m str ''

does not detect that a cookie/field is empty ?

Running the attached 'hdrs' script against the attached haproxy.cfg sees :
===
...
cookie: cook2hdr=#####
bar: bar
baz: baz
meta: ,bar,baz
foo:
===
when foo: should not be created, and meta: should only have 2 fields.

Am I just getting the idiom/incantation wrong ?

[ stock/current haproxy 2.6 from Debian/Ubuntu LTS backports ]

hdrs
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haproxy.cfg
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