4.7.3 No Null Values

Every property must have a value. The range of property states does not include having a “null value”, or “no value”. Setting a property to “null” is equivalent to removing that property. In the case of multi-value properties, the setting of a particular value within the array to null results in the removal of that value and the compacting of the array. As a result it is possible to have a multi-value property with no values (an empty array). See 7.1.5 Adding and Writing Properties.