null is a special value that indicates no value was entered in an input field or no value was extracted via a lookup. For example, null is used when a related record was not found. Null does not compare to anything, including null itself. The result of a comparison to null is always false. Arithmetic and logical operations on null also return null, as do most functions. To check whether a value is null, use the IsNull function.
The IsNull function, as its name implies, is used to check whether a field contains any data, returning only true or false values.
Since the IsNull function yields true or false results, it can be broadly used to set conditions in conditional functions. For instance, the formula
If(IsNull([Company Name]), ToUser("email@example.com")) could be used for the Lead Owner column to assign all leads where the company name is undefined to a specific user – Sam Powter.
The meaning of the IsNull function can be inverted by using "not" before the function name. For example, the formula
If(not IsNull([Project Manager]), "Assigned") used for the Project Status column has the following interpretation: if the Project Manager field in the project record is not empty, then the project status is changed to "Assigned".
If you wish to perform operations with a field value but are uncertain whether the field is empty or not, the Nz function is used: if the verified field is empty, this function returns its second argument. This approach allows you to handle certain difficulties with simple arithmetic operations and others. The function is applicable to various field types.