Recognizing and setting of NULL values in table editor

Within the "Database Tools and SQL" plugin of PyCharm I opened a table in the editor, so all columns and rows are shown in a spreadsheet like way. Unfortunately, cells with the value NULL look exactly the same as cells with an empty string. And when editing these cells, I can enter arbitrary values, yet I cannot explicitly set the value to NULL. I couldn't find any option to alter this behavior in the Tools → Database → Data Views preference pane.

How can I work with NULL values?