Numbers: VALUE function does not recognize empty string

I am using Apple Numbers and find it frustrating that cell arguments containing empty text (and sometimes contain numbers from other sheets) are not converted to a number of value 0, when referenced by a function that expects a numeric value.

For example, a function in cell:

=MAX(I5,0.5×J5)

with J5 being empty, yields an error message

The operator “*” expects a number but found “.”

So I tried to encase J5 with VALUE(J5), and got another message:

VALUE requires a string specifying a number, but found “” instead.

Is there an efficient way to treat all spaces as 0 for the countless cells that may have that situation?