Is there any specific way to set an empty blob in SQLite?

So I'm making a contact list program and I'm implementing the use of photos in the form of BLOBs for the database (SQLite), I can easily set a BLOB to an entry (that would be, by default empty) and retrieve it. However when I can't seem to figure out how to set the BLOB as empty again (using the UPDATE query). (I have tried to set a byte array as null but that just gives me a NullPointer error)