title: Checkout error with working tree clean
body: <p>Please, 
  I get the error "Your local changes to the following files would be overwritten by checkout" but my working tree is clean.</p>
  
  <p>does anyone have any idea of what is going on here?</p>
  
  <pre><code>$ git status
  On branch experiment
  nothing to commit, working tree clean
  
  $ git checkout develop
  error: Your local changes to the following files would be overwritten by checkout:
  app/build.gradle
  Please commit your changes or stash them before you switch branches.
  Aborting
  </code></pre>
  
  <p>(the file <code>app/build.gradle</code> is not in my <code>.gitignore</code> file)</p>
  
  <hr>
  
  <p>This is the top level .gitignore file:</p>
  
  <pre><code>### Android ###
  
  # Built application files
  *.apk
  *.ap_
  
  # Files for the ART/Dalvik VM
  *.dex
  
  # Java class files
  *.class
  
  # Generated files
  bin/
  gen/
  out/
  
  # Gradle files
  .gradle/
  build/
  
  # Local configuration file (sdk path, etc)
  local.properties
  
  # Proguard folder generated by Eclipse
  proguard/
  
  # Log Files
  *.log
  
  # Android Studio Navigation editor temp files
  .navigation/
  
  # Android Studio captures folder
  captures/
  
  # Intellij
  .idea
  *.iml
  
  # Keystore files
  *.jks
  
  # External native build folder generated in Android Studio 2.2 and     later
  .externalNativeBuild
  
  # Mac
  .DS_Store
  
  ### Android Patch ###
  gen-external-apklibs
  </code></pre>
  
  <hr>
  
  <p>This is a .gitignore file inside the /app directory (I don't know why it is there):</p>
  
  <pre><code>build
  
  # Secrets
  secrets.properties
  </code></pre>