non-serializable value detected in an action

[AdamWP]

Environment: Ubuntu 20.04, Node 17.01, NPM 8.1.0. (Also tested with same result on Node 12, 16 & 18 and NPM 9.2.0). Tried Chrome and Safari with same results.

index.js:1 A non-serializable value was detected in an action, in the path: register. Value: ƒ register(key) {
pStore.dispatch({
type: constants__WEBPACK_IMPORTED_MODULE_1["REGISTER"],
key: key
});
}