How to exclude NULL values

[Mch201]

I have an excel table with weekly grades with students names. and in the last row, it indicates if the student grades dropped significantly recently or no. only few of the grades dropped insignificantly. What expression or formula can I use to only show the grades that have dropped recently in a Qlik sense chart 

[micheledenardi]

Please add some example data and what you expect to see in your chart.