Handing keys in environment

[alexbuhl]

I am unsure how to use keys in the declaration of environments. How
does one handle the case when the user supplies or does not supply
the key-value pairs ?

\documentclass[a4paper,10pt]{article}

\ExplSyntaxOn

\tl_new:N \tlapis_kl_tl
\tl_new:N \tlapis_lv_tl

\keys_define:nn { tlapis_keys }
{
kl .tl_set:N = \tlapis_kl_tl,
kl .default:n = {red},
kl .initial:n = {red},

lv .tl_set:N = \tlapis_lv_tl,
lv .default:n = {},
lv .initial:n = {},
}

\NewDocumentEnvironment {wvTlapis} { o }
{
\tl_if_novalue:nF {#1}
{ \keys_set:nn {tlapis_keys} {#1} }
}
{ }

\ExplSyntaxOff

\begin{document}

\end{document}
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