Could not get unknown property 'release' for SigningConfig container of type org.gradle.api.internal


問題の説明
Could not get unknown property 'release' for SigningConfig container of type
 org.gradle.api.internal.FactoryNamedDomainObjectContainer.

理由: module buildTypes{} signingConfig signingConfigs.release, , signingConfigs{} buildType{} , , , signingConfigs{} release .
以下のように、コンパイルは1、 signingConfigs {}。 2、 signingConfigs{} buildTypes{}
signingConfigs {

        debug{
            storeFile file('xxx')
            storePassword '***'
            keyAlias 'xxx'
            keyPassword '***'
        }

        release {
            storeFile file('xxx')
            storePassword '***'
            keyAlias 'xxx'
            keyPassword '***'
        }

    }

    buildTypes {
        debug {
            //      
            minifyEnabled true
            //        
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            //
            signingConfig signingConfigs.debug
        }

        release {
            //    zip
            zipAlignEnabled true
            //      resource  
            shrinkResources true
            //      
            minifyEnabled true
            //        
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            //
            signingConfig signingConfigs.release
        }
    }