[MC-279950] Modifying command data storage throws an error

Create a data storage

/data merge storage example:temp {foo:123}

Try to modify the data storage

/data merge storage example:temp {bar:123}

Linked issues

Can confirm

Can confirm, as well as it causing functions to halt execution as if a `return` command was run

Interestingly, using data modify will modify the storage, even if the effects are otherwise identical:

/data modify storage example:temp {} merge value {bar: 123}

(The error still happens, though.)

Dang, puts my datapack work on pause. Worth noting, /data remove has the same error-despite-working thing.

Can confirm. I can't set any data at all; my functions are failing with a generic java.lang.UnsupportedOperationException error.