newton 1st law is valid in absence of net force or not?

" A body will move in a straight line with a constant speed UNLESS acted upon by a force"
The LAW specifically includes a reference to a net force of zero.
As being the primary meaning of that law.
The UNLESS part states that this first law is limited to those situations in which the net force is zero and does not apply to other situations.

Newton's first law is thus definitely valid and applicable.

In case that "in the absence of net force" means "there is no force acting on the object". In other words, the net force is zero.

Thus, Newton first low is valid.