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CF9 ORM relationships – hasProperty oddity

In my CF9 ORM application, I have a magazine object. Each magazine has a single genre (e.g. Craft, Sports, etc.) – so I have a many-to-one relationship set up on the magazine.cfc:

component output="false" persistent="true"
{
	// identifier
	property name="magazineid" fieldtype="id" setter="false" generator="identity";
	
	// properties
	property name="title";
	property name="genre" cfc="genre" fieldtype="many-to-one" fkcolumn="frn_genreid";
}

The genre.cfc looks like this:

component output="false" persistent="true"
{
	// identifier
	property name="genreid" fieldtype="id" setter="false" generator="identity";
	
	// properties
	property name="genre";
	property name="magazines" cfc="magazine" fieldtype="one-to-many" fkcolumn="frn_genreid";
}

It all works nicely, until I want to try removing the genre from the magazine.

If I create a new magazine entity, the genre property contains an empty string (confirmed by dumping the object). And the hasGenre() method returns false.

If I load an existing magazine entity, the genre property contains a genre object, and hasGenre() returns true.

So to try to remove the genre, I use:

magazine.setGenre( '' );

to set the genre property to an empty string, just like in the new entity – but hasGenre() still returns true – why?

If I instead use:

magazine.setGenre( {} );

to set the genre property to an empty struct, hasGenre() now returns false, and everything works OK.

But what is the difference between the empty string that I set manually, and the empty string that’s present when a new entity is created? And why do they return different results for hasGenre()?