How to reproduce:
1. Create an empty project
2. Edit your Packages/manifest.json to include "com.unity.addressables": "0.1.2-preview"
3. Click Window -> Asset Management -> Addresable Assets
4. In the Addressables window click Create Addressables Settings
5. Observe the errors in the Console window

Expected result: Addressables Settings are created successfully
Actual result: Creating Addressables Settings results in errors

Addressables System was introduced in Unity 2018.2

Reproducible with: 2018.2.0b5, 2018.2.0f2

Cannot be tested on 2018.3.0aX due to Package Manager errors

Note: the issue only occurs with 0.1.2 Addressables System version