Typed input field, data type number: empty

In an inject node (and any other node with typed input) I am able to select "number" as type and leave the field blank. I would expect that this is not valid but instead the node is saved.

Why (saved, no error)?

Wouldn't it been better to throw an error or provide 0 as initial value - similar to boolean where true is the initial value. It seems that 0 is saved but not show in the dialog field.