There are two approaches you can try to filter out lines:
awk 'NF' data.txt
and
awk 'length' data.txt
Just put these at the start of your command, i.e.,
awk -v variable=$bashvariable 'NF { print variable ... }' myinfile
or
awk -v variable=$bashvariable 'length { print variable ... }' myinfile
Both of these act as gatekeepers/if-statements.
The first approach works by only printining out lines where the number of fields (NF) is not zero (i.e., greater than zero).
The second method looks at the line length and acts if the length is not zero (i.e., greater than zero)
You can pick the approach that is most suitable for your data/needs.