Steps to reproduce:

• Open clean qtquickview_(kotlin or java)
• Define:
  • qtPath with own build qt host path 
• Make sure PATH does not have Ninja or edit the path to be wrong
• Make sure ~/Qt/Tools/Ninja does not exist or edit the path to be wrong
• Run application, it should fail and give you the error below

Bolded the misleading part of the error: 

Execution failed for task ':app:QtBuildTask'.
> No valid path to Ninja found. Checked locations:
      - Manually specified path in build.gradle QtBuild extension: C:\Repos\Qt\Tools\Ninja\ninja.exe
      - Environment PATH
      - Default Qt installation directory: C:\Repos\Qt\Tools\Ninja

Like in QTTA-256 there is no "C:\Repos\Qt\Tools\Ninja\ninja.exe" to be found so we should give a different error here. File missing or something and figure how to differentiate between custom build host and one gotten from Installer.