How to omit blank cells when calculating weighted averages

Hello, new to Excel and need help with function.
I am calculating grades for my students, and if they were absent, I do not
want them penalized. What function will omit the blank cells when the formula
is calculating the weighted average? I tried the average option but it still
treated the cell as a zero.

Here is the formula:
=((B5*$B$2)+(C5*$C$2)+(D5*$D$2))

When I tried removing the section of the formula for students who were
missing the assignment in B5, the average still remained low. Thanks in
advance!!