title: Issue building apk file
body: <p>I am working with an Application where I enabled runProguard true in my build.gradle file of my app. When I go for building signed apk I am getting warnings and build process failed. </p>
  
  <p><strong>Log File:</strong></p>
  
  <pre><code>Warning:com.google.common.base.Absent: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Ascii: can't find referenced class javax.annotation.CheckReturnValue
  Warning:com.google.common.base.CaseFormat$StringConverter: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.CharMatcher: can't find referenced class javax.annotation.CheckReturnValue
  Warning:com.google.common.base.Converter: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Converter$ConverterComposition: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Converter$FunctionBasedConverter: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Converter$ReverseConverter: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Defaults: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Enums$StringConverter: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Equivalence: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Equivalence$EquivalentToPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Equivalence$Wrapper: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.FinalizableReferenceQueue$FinalizerLoader: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Function: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.FunctionalEquivalence: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$ConstantFunction: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$ForMapWithDefault: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$FunctionComposition: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$FunctionForMapNoDefault: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$IdentityFunction: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$PredicateFunction: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Functions$SupplierFunction: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Joiner: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Joiner: can't find referenced class javax.annotation.CheckReturnValue
  Warning:com.google.common.base.Joiner$1: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Joiner$MapJoiner: can't find referenced class javax.annotation.CheckReturnValue
  Warning:com.google.common.base.MoreObjects: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.MoreObjects$ToStringHelper: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Objects: can't find referenced class javax.annotation.CheckReturnValue
  Warning:com.google.common.base.Objects: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Objects$ToStringHelper: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Optional: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.PairwiseEquivalence: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Preconditions: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$AndPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$AssignableFromPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$CompositionPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$ContainsPatternPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$InPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$InstanceOfPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$IsEqualToPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$NotPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$ObjectPredicate$1: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$ObjectPredicate$2: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$ObjectPredicate$3: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$ObjectPredicate$4: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Predicates$OrPredicate: can't find referenced class javax.annotation.Nullable
  Warning:com.google.common.base.Present: can't find referenced class javax.annotation.Nullable
  </code></pre>
  
  <p>build.gradle </p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
  
      signingConfigs {
  
      }
      compileSdkVersion 21
  
      buildToolsVersion '20.0.0'
  
      defaultConfig {
  
          minSdkVersion 15
  
          targetSdkVersion 21
  
          versionCode 1
  
          versionName '1.0'
  
      }
      buildTypes {
  
          release {
  
              runProguard true
  
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 
  
  'proguard-rules.pro'
          }
  
      }
      productFlavors {
  
      }
          packagingOptions {
  
              exclude 'META-INF/LICENSE.txt'
  
              exclude 'META-INF/NOTICE.txt'
          }
  
  }
  
  dependencies {
  
      compile fileTree(dir: 'libs', include: ['*.jar'])
  
      compile 'com.google.guava:guava:18.0'
  
      compile 'com.google.code.gson:gson:2.3'
  
      compile 'com.microsoft.azure:azure-mobile-services-android-sdk:2.0.2-beta+'
  
      compile (group: 'com.microsoft.azure', name: 'azure-notifications-handler', version: '1.0.1', ext: 'jar')
  
      compile project(':library')
  
      compile project(':StyleableDateTimePicker-master')
  
      compile 'com.facebook.android:facebook-android-sdk:3.23.+'
  
      compile 'com.android.support:support-v4:22.0.0+'
  
      compile 'com.android.support:appcompat-v7:22.0.0'
  
      compile 'com.google.android.gms:play-services:6.5.87'
  
      compile 'com.github.navasmdc:MaterialDesign:1.+@aar'
  
      compile 'com.android.support:recyclerview-v7:21.0.0'
  
      compile 'com.android.support:cardview-v7:21.0.+'
  
      compile 'com.melnykov:floatingactionbutton:1.1.0'
  
      compile 'com.ToxicBakery.viewpager.transforms:view-pager-transforms:1.1.0@aar'
  
      compile 'de.hdodenhof:circleimageview:1.2.2'
  
      compile 'com.github.alamkanak:android-week-view:1.2.1'
  
      compile('ch.acra:acra:4.5.0') {
  
          exclude group: 'org.json'
      }
  
      compile 'com.github.machinarius:preferencefragment:0.1.1'
  
  }
  </code></pre>