Default value "" in schema will cast to undefined

[GoodGuyGoose]

When setting a property's value to an empty string in a schema, the schema will cast the value to undefined rather than retain the empty string. E.g:

"composition": {"\\$type": "string", "default": ""}
// will return undefined

[kjellmorten]

I tried to replicate this, @GoodGuyGoose, but was not able to find the cause for it within the Integreat package. Here's the tests I wrote to verify: a51dce1

Perhaps this is something that happens in the integreat-server package or due to some other gotcha in the mutations.