[Bug] Cannot exclude specific files

**Describe the bug**
I've built a .NET Core web API application. When executing docfx init, it successfully generates documentation hosted on localhost. However, I encounter an issue when trying to exclude files in the 'Services' folder. The output during the build process appears as follows:

`No files are found with glob pattern images/**, excluding , under directory "D:\CS\SpeechSeek"`

Shouldn't it also indicate excluding "_site/**" and whatever I specify in docfx.json? Regardless of the patterns I specify in docfx.json, the 'excluding' information is always null. I need to exclude a couple of folders from the documentation generation.

**This is my _docfx.json:_**
```
{
"metadata": [
{
"src": [
{
"src": "../Speechseek",
"files": [
"**/*.csproj"
]
}
],
"dest": "api"
}
],
"build": {
"content": [
{
"files": [
"**/*.{md,yml}"
],
"exclude": [
"_site/**", <-- no excluded??
"Services/** <-- no excluded??
]
}
],
"resource": [
{
"files": [
"images/**"
]
}
],
"output": "_site",
"template": [
"default",
"modern"
],
"globalMetadata": {
"_appName": "speechseek",
"_appTitle": "speechseek",
"_enableSearch": true,
"pdf": false
}
}
}
```

**Conclusion:**

docfx builds the documentation but not excluding specific folders and .cs files

I want to remove this files