Conditional Formatting based on dates

I wanted to highlight an entire row based on the date in a column. Yellow if it's equal to today, Red if it's past 4 days from today, and Green if it's sooner than today.
I used these formulas and they worked:

=TODAY()=$M2 (Yellow)
=TODAY()+4>=$M2 (Red)
=TODAY()<=$M2 (Green)

Only problem is that I want the rows to remain blank if there is nothing in the M column and they all appear red. The column has a formula K2+L2 (Where column K is the date where an invoice is sent and column L are the net terms) and the default date that appears is 1/0/00. All those rows are red and I need them blank, until data is entered into columns K and L. Hope that makes sense.

I think the default date is 01/01/1900 you could always set conditional formatting based on that specific date.

= 01/01/1900 (No formatting)

I entered that as a condition and it brought back an error. Do I need to enter the formula a particular way?

I tried changing the formula to check for empty cells and it worked as long as I erased what was in the cell, but since I have a simple sum formula (K2+L2) in that column it remains red. I can always drag the formula down as I go, but would rather find a fix around that. Can I add a new condition to leave the row blank if all that's in there is the formula, without it converting to an actual date once I populate columns K and L?

I have attached the file for your review. Thank you so much for all your help.

Create a new rule and the code is
=$M2=0
and make sure the background is White (not blank)
make the rule the top most rule

Beautiful! That did it. Thank you so much for all your assistance and patience with my issue.