V4: ionic generate class fails immediately on new blank app.

# Bug Report

**Ionic Info**

```
Ionic:

ionic (Ionic CLI) : 4.0.2

System:

NodeJS : v8.11.3
npm : 6.2.0
OS : Windows 10
```

**Describe the Bug**
Immediately after creating a new blank application, I run `ionic generate class career`, it produces:
Tree type is not supported.
[ERROR] Could not generate class.

**Steps to Reproduce**
Steps to reproduce the behavior:
1. Create a brand new blank ionic application.
2. Go to terminal, type ionic generate class career.
3. See error

**Related Code**
None.

**Expected Behavior**
Create a class somewhere in project structure called career.ts.

**Additional Context**
None.

Start by creating a new blank Ionic application and reproducing `ionic generate class career` on the reported environment. Trace the CLI's generate-class handling from that command and verify that it creates a `career.ts` file somewhere in the project structure without the “Tree type is not supported” error.

Escrito por el modelo de indexación a partir del texto del issue.