In some scenarios after ApiUpdater runs old, non existing namespaces may be left in using clauses.

This may happen if Unity changes a type to a namespace that already exists and is already imported in the script.

For instance, consider the following:

// In UnityEngine.dll
namespace UnityEngine.Foo
{
class Bar {}

class Baz {} // Originally in UnityEngine.Other
}

// in user code
using UnityEngine.Foo;
using UnityEngine.Other;

class C : UnityEngine.Other.Baz
{
}

When ApiUpdater finishes updating user code it will looks something like:

// in user code
using UnityEngine.Foo;
using UnityEngine.Other; // Should have been removed

class C : Baz
{
}