MosaicId can be instantiated with undefined

[decentraliser]

https://github.com/nemtech/nem2-sdk-typescript-javascript/blob/dc6135d141b4d3de75fac8f64ed38705c92d59ce/src/model/mosaic/MosaicId.ts#L52

new MosaicId(undefined) does not throw an error. As a consequence, it is possible to create a transaction with an empty Mosaic object.