Section 11.2.3 states that

"If the property is single-valued and has the null value, the service responds with 204 No Content."

This is understandable for complex properties, but somewhat odd for primitive properties as the obvious representation for a null value would be

{
"@odata.context":"$metadata#SomeThings(1)/SomeProperty",
"value":null
}

The benefit of this representation is that it may contain instance annotations for the property.