The setToNull operator is an Executable Action Language (EAL) command that explicitly clears the value of a nullable attribute or a single-link association (0..1). It is the programmatic way to assign a database NULL to a field.

Syntax

[Object].[NullableProperty].setToNull

Example

Order.allinstances->first.OrderDate.setToNull

The OrderDate for that specific order is wiped and becomes empty.

You can also use the assign operator := and assign <Type>.nullValue to get the same effect.

Error Message	Cause	Solution
"setToNull can only be applied to nullable attributes"	Mandatory Property: The attribute or association is marked as "Required" or multiplicity "1" in the model.	In the Class Diagram, under Mode, the "Allow Null" box in the properties should be set to true, or the multiplicity should be changed to 0..1.
"setToNull can only be applied to nullable attributes"	Collections: You are trying to use it on a list (0..*) instead of a single object.	Use the ->clear operator to empty a list.