SQLcl: Make NULLs “visible”Posted: March 12, 2017
One of the nice features in SQL Developer is to be able to define a value to replace NULLs (for display purpose only) in the data grids. Jeff Smith has a blog post about it in case you are interested.
You can achieve something similar in your SQLcl session by using set null some_string.
And here is the output from a query after setting the system variable.