When [1] was introduced, we prevented to define a 'null' value for a
parameter P in a palette and forced a fallback to a default value X
defined in a "base" palette (value X which could be null). That allowed
to ensure that all final palette values were consistent as always
fallbacking to a "safe" value. However, since then, we introduced [2]
which makes it so a parameter P in the "base" palette is defined to X
(not null) while null is a valid value for P. We could keep the old
system and define that paramater P to a 'null' value in the "base"
palette and add the default X value in all palettes explicitely... but
with this commit we are choosing to be less tolerant (but in fact more
tolerant to custo) and rely on the fact palettes are well defined with
valid values (e.g. not defining a value to null while only X or Y are
allowed for example). Indeed, an exception for the "null" value did not
make much sense: if only X or Y are allowed as value for a parameter P,
setting a random Z value was not prevented, only null was.
[1]: https://github.com/odoo/odoo/commit/05d17089c4a604cb49f1a263b68f39aeffecccda
[2]: https://github.com/odoo/odoo/commit/a48a30f954afcb6ff3a59c4f32b05fd0c2cfcd2b
Part-of: odoo/odoo#76033
qsm-odoo
0ebf956edb