Is it allowed to set the value to null on a mandatory property in an EventType?|OPC UA Standard|Forum|OPC Foundation

If a mandatory field has a nullable value you could set it to. i..e String to ""

But the Value cannot be Variant.Empty for mandatory properties.

However, the "" rule does not apply if the description of the property makes it clear that "" is not a valid value:

SourceName provides a description of the source of the Event. This could be the string-part of the DisplayName of the Event source using the default locale of the server, if the Event is specific to a Node, or some server-specific notation.

(i.e. "" is not a description)

Clients should be designed defensively to deal with misbehaving Servers but that does not make the server right.

https://reference.opcfoundatio.....ionType%2E

ConditionName identifies the Condition instance that the Event originated from. It can be used together with the SourceName in a user display to distinguish between different Condition instances. If a ConditionSource has only one instance of a ConditionType, and the Server has no instance name, the Server shall supply the name element of the BrowseName of the ConditionType.

Specification says no and provides a default if it does not make sense.