Errors running builder 'CDT Builder' when trying to build OpenCV for android samples

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Hello guys I'm trying to learn about openCV in android I've already following the instruction given http://docs.opencv.org/doc/tutorials/introduction/androidbinarypackage/androidbinarypackageusingwith_NDK.html

but when I'm trying to compile I'm only getting

01:50:14 ** Auto Build of configuration Default for project org.opencv.samples.fd.FdActivity 
** "C:\Android\android-ndk-r8\ndk-build.cmd" 
Install: libdetection_based_tracker.so => libs/armeabi-v7a/libdetection_based_tracker.so

01:50:14 Build Finished (took 184ms)

in the console and I'm also get an error

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

anyone ever encountered this problem before? please help me to solve this problem

thank you