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.

先建立一個新的空白 Ionic 應用程式，並在回報的環境中重現 `ionic generate class career`。從該命令開始追蹤 CLI 對 generate-class 的處理，並確認專案結構中的某個位置會建立 `career.ts` 檔案，且不會出現「Tree type is not supported」錯誤。

由索引模型根據 Issue 內容生成。