title: Errors running builder 'CDT Builder' when trying to build OpenCV for android samples
body: <p>Hello guys I'm trying to learn about openCV in android
  I've already following the instruction given <a href="http://opencv.itseez.com/doc/tutorials/introduction/android_binary_package/android_binary_package_using_with_NDK.html#android-binary-package-with-ndk">here</a></p>
  
  <p>but when I'm trying to compile I'm only getting </p>
  
  <blockquote>
    <p>01:50:14 <strong>** Auto Build of configuration Default for project
    org.opencv.samples.fd.FdActivity **</strong>
    "C:\Android\android-ndk-r8\ndk-build.cmd"  Install:
    libdetection_based_tracker.so =>
    libs/armeabi-v7a/libdetection_based_tracker.so</p>
    
    <p>01:50:14 Build Finished (took 184ms)</p>
  </blockquote>
  
  <p>in the console
  and I'm also get an error</p>
  
  <blockquote>
    <p>Errors occurred during the build. Errors running builder 'CDT Builder'
    on project 'org.opencv.samples.fd.FdActivity'. Internal error building
    project org.opencv.samples.fd.FdActivity configuration Default
    java.lang.NullPointerException Internal error building project
    org.opencv.samples.fd.FdActivity configuration Default
    java.lang.NullPointerException</p>
  </blockquote>
  
  <p>anyone ever encountered this problem before?
  please help me to solve this problem</p>
  
  <p>thank you </p>