In Part 6 V 1.04 and 1.05 is the following described:

5.1.6 Variant (V1.04)
• A Variant is a union of all built-in data types including an ExtensionObject. Variants can also contain arrays of any of these built-in types. Variants are used to store any value or parameter with a data type of BaseDataType or one of its subtypes.
• Variants can be empty. An empty Variant is described as having a null value and should be treated like a null column in a SQL database. A null value in a Variant may not be the same as a null value for data types that support nulls such as Strings. Some DevelopmentPlatforms may not be able to preserve the distinction between a null for a DataType and a null for a Variant, therefore, applications shall //not// rely on this distinction. This requirement also means that if an Attribute supports the writing of a null value it shall also support writing of an empty Variant and vice versa.
• …

5.1.7 Variant (Draft 1.05.25 – latest Draft on sharepoint)
• A Variant is a union of all built-in data types including an ExtensionObject. Variants can also contain arrays of any of these built-in types. Variants are used to store any value or parameter with a data type of BaseDataType or one of its subtypes.
• Variants can be empty. An empty Variant is described as having a null value and should be treated like a null column in a SQL database. A null value in a Variant may not be the same as a null value for data types that support nulls such as Strings. Some DevelopmentPlatforms may not be able to preserve the distinction between a null for a DataType and a null for a Variant, therefore, applications shall //not// rely on this distinction. This requirement also means that if an Attribute supports the writing of a null value it shall also support writing of an empty Variant and vice versa.
• …