The default missing value is a system option.
Options missing=' ';
before the Proc Report code would display a blank character for missing values in the report output.
reset to the default behavior using
options missing='.';
after the proc report.
Actually "suppressing cells" wouldn't make much sense in report output as that might tend to shift things around a lot. A more concrete of example of what your currently getting and what the desired appearance would be might generate suggestions. Data in the form of a data step and your report code using that data would be needed.