Left Join Not Working in Crystal Report

If there are two tables linked with a Left Join and you would like to filter the dataset on a field in the optional table but no rows are retrieved when the field in question is Null, you need to verify the following:

Crystal Reports overrides any Left Join to an Inner Join if there is a WHERE clause referencing the dependent table. Test for the Null condition before testing for the condition you are evaluating for.

For example: (IsNull({table.field}) OR {table.field} = "value")

As a habit, make sure to always enclose the condition in parenthesis for proper evaluation.