Can't sign APK because of third party library

Question

This is my first app publication. The project is working fine in the development side, but I am facing a problem during signing APK.

Included library in the app of com.1gravity:android-contactpicker

and facing problem during signing apk only.

error coming

Error:(30, 44) error: package com.onegravity.contactpicker.contact does not exist

and

Generate Signed APK: Errors while building APK. You can find the errors in the 'Messages' view.

gradle file

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "26.0.0"
    defaultConfig {
        applicationId 'com.mymatatu'
        minSdkVersion 15
        targetSdkVersion 25
        versionCode 3
        versionName "1.3"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }

    productFlavors {
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    debugCompile project(':library')
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile 'com.android.volley:volley:1.0.0'
    compile 'com.android.support:design:25.3.1'
    compile 'com.android.support:support-v4:25.3.1'
    compile 'com.android.support:cardview-v7:25.3.1'
    compile 'com.android.support:recyclerview-v7:25.3.1'
    compile 'com.github.bumptech.glide:glide:4.0.0-RC1'
    compile 'com.github.markushi:circlebutton:1.1'
    testCompile 'junit:junit:4.12'
    annotationProcessor 'com.github.bumptech.glide:compiler:4.0.0-RC1'
}

Answer 1

in your gradle file change this

debugCompile project(':library') 

line into

compile project(':library')