Since 1.472+ it has been possible to configure the master node's own properties.
There are some node properties that do not make sense as a global node property. Up until Jenkins 1.472 the way to mark properties as such was to return false from NodePropertyDescriptor.isApplicable(clazz) if clazz instanceof Jenkins
That technique no longer works as that also means that the property cannot be configured as a node property of the master directly.
There needs to be an alternative mechanism for differentiating properties that can be applied to all nodes from properties that can be applied to the master node.