Signed APK cannot generated in Android Studio 1.3

Question

I have integrated MuPdf library as module in my app. When I was generating Signed Apk it didn't generate and it shows the following errors..

Information:Gradle tasks [:app:assembleRelease]

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for debug as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for debug as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for debug as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for debug as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for release as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for release as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for release as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

Warning:Dependency org.apache.httpcomponents:httpclient:4.3.5 is ignored for release as it may be conflicting with the internal version provided by Android.
         In case of problem, please repackage it with jarjar to change the class packages

:Mupdf:compileLint
:Mupdf:copyReleaseLint UP-TO-DATE
:Mupdf:preBuild UP-TO-DATE
:Mupdf:preReleaseBuild UP-TO-DATE
:Mupdf:checkReleaseManifest
:Mupdf:preDebugAndroidTestBuild UP-TO-DATE
:Mupdf:preDebugBuild UP-TO-DATE
:Mupdf:prepareComAndroidSupportAppcompatV72211Library UP-TO-DATE
:Mupdf:prepareComAndroidSupportSupportV42211Library UP-TO-DATE
:Mupdf:prepareReleaseDependencies
:Mupdf:compileReleaseAidl UP-TO-DATE
:Mupdf:compileReleaseRenderscript UP-TO-DATE
:Mupdf:generateReleaseBuildConfig UP-TO-DATE
:Mupdf:generateReleaseAssets UP-TO-DATE
:Mupdf:mergeReleaseAssets UP-TO-DATE
:Mupdf:generateReleaseResValues UP-TO-DATE
:Mupdf:generateReleaseResources UP-TO-DATE
:Mupdf:mergeReleaseResources UP-TO-DATE
:Mupdf:processReleaseManifest UP-TO-DATE
:Mupdf:processReleaseResources UP-TO-DATE
:Mupdf:generateReleaseSources UP-TO-DATE
:Mupdf:compileReleaseJava UP-TO-DATE
:Mupdf:extractReleaseAnnotations UP-TO-DATE
:Mupdf:mergeReleaseProguardFiles UP-TO-DATE
:Mupdf:compileReleaseNdk UP-TO-DATE
:Mupdf:packageReleaseJniLibs UP-TO-DATE
:Mupdf:packageReleaseRenderscript UP-TO-DATE
:Mupdf:packageReleaseResources UP-TO-DATE
:Mupdf:proguardRelease UP-TO-DATE
:Mupdf:bundleRelease UP-TO-DATE
:app:preBuild UP-TO-DATE
:app:preReleaseBuild UP-TO-DATE
:app:checkReleaseManifest
:app:preDebugBuild UP-TO-DATE
:app:prepareComAndroidSupportAppcompatV72211Library UP-TO-DATE
:app:prepareComAndroidSupportSupportV42211Library UP-TO-DATE
:app:prepareProductManagementMupdfUnspecifiedLibrary UP-TO-DATE
:app:prepareReleaseDependencies
:app:compileReleaseAidl UP-TO-DATE
:app:compileReleaseRenderscript UP-TO-DATE
:app:generateReleaseBuildConfig UP-TO-DATE
:app:generateReleaseAssets UP-TO-DATE
:app:mergeReleaseAssets UP-TO-DATE
:app:generateReleaseResValues UP-TO-DATE
:app:generateReleaseResources UP-TO-DATE
:app:mergeReleaseResources UP-TO-DATE
:app:processReleaseManifest UP-TO-DATE
:app:processReleaseResources UP-TO-DATE
:app:generateReleaseSources UP-TO-DATE
:app:compileReleaseJava

 cannot find symbol class MuPDFCore

 cannot find symbol class MuPDFPageAdapter

 cannot find symbol class OutlineActivityData

 cannot find symbol class ReaderView

 cannot find symbol class ReaderView

 cannot find symbol class MuPDFCore

 cannot find symbol class MuPDFCore

 cannot find symbol class ReaderView

 cannot find symbol class MuPDFPageAdapter

 cannot find symbol class MuPDFCore

 cannot find symbol variable OutlineActivityData

Can anyone help me to solve this problem?

Here is my build.gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "MyProjectPackageName"
        minSdkVersion 11
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
   }

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:21.0.0'
    compile 'com.google.zxing:zxing-parent:3.2.0'
    compile 'com.google.zxing:zxingorg:3.2.0'
    compile 'com.google.zxing:javase:3.2.0'
    compile 'com.google.zxing:core:3.2.0'
    compile 'com.google.zxing:android-integration:3.2.0'
    compile 'com.google.zxing:android-core:3.2.0'
    compile 'com.google.zxing:zxing.appspot.com:3.2.0'
    compile 'com.google.zxing:glass-mirror:2.3.0'
    compile project(':Mupdf')
    compile 'org.apache.httpcomponents:httpmime:4.3.5'
    }