As a user, you may want to perform some tests with blank data as parameters.
For example, a validation test to check that the user name field cannot be blank, will require a blank value to be passed to the WebEdit type of object. This can be achieved with the help of Empty Data Handling feature.
Blank data can be passed to both, Static as well as Data sheet parameters in the following way:
Static
Use tilde sign within double quotes "~" to pass a blank value as static data.
Data Sheet Parameter
Enter $NULL$ in the data sheet for the required parameter to pass a data sheet parameter as blank value. By default, the first time a user opens the data sheet, $NULL$ will be displayed appears for all parameters.
You 
You should not execute test cases with the default data sheet values. The data sheet is required to be opened and attached at least once prior to execution.
An 
An empty cell in the data sheet acts as a breakpoint for tasks and should be used for passing blank values to actions parameters.