Misleading useNull flag

[engi2nee]

In the InstantiatorConfig we can pass useNull as false, which I expected to fill all nullables with random values.

Then I noticed In the Readme: If config.useNull = false then InstanceFactor will be called to decide if a null or non-null value is returned.

digging into the code base, I found toNullableInstanceFactory which is set to use ToNullableInstanceFactoryMode.RANDOM (Randomly return null or a Random value) in all default nullable factories inside DEFAULT_INSTANCE_FACTORIES, with no way to change it except for new custom factories.

I think useNull boolean flag should be replaced by a ToNullableInstanceFactoryMode check, as there is no way to make default nullable factories never return null.