I stumbled on the following quirk recently:

\tl_clear:N \l_tmpa_tl
\fp_eval:n { round( \l_tmpa_tl, 4) }

gives 4 as the answer (or whatever the rounding value is). Usually, in 
the situation where this arose, \l_tmpa_tl is a string of digits 
possibly including a decimal point. In this instance it was empty. Okay, 
I can check for that, but I wonder if l3fp should do so, and either give 
an error, as

\fp_set:Nn \l_tmpa_fp { \l_tmpa_tl }

does when the token list is empty, or give a conventional 0 as answer?


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