即使使用-keep类,仍然有错误未解析的引用

package com.xyz.demo

import android.content.Context
import com.facebook.stetho.Stetho
import com.facebook.stetho.okhttp3.StethoInterceptor
import okhttp3.Interceptor

object OptionalDependencies {

    fun initStetho(context: Context) {
        Stetho.initializeWithDefaults(context)
    }

    fun getNetworkInterceptor() : Interceptor?  = StethoInterceptor()

}

在StartActivity.kt中

package com.xyz.demo.ui

import com.xyz.demo.OptionalDependencies
……

class StartActivity : AppCompatActivity() {

    private fun initStetho(@ApplicationContext appContext: Context) {

        val interceptor : Interceptor? = 
                OptionalDependencies.getNetworkInterceptor()//<=== any where will get error referring the 
        ……
    }

    ……
}

在build.gradle中

buildTypes {
    debug {
        minifyEnabled true
        shrinkResources true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

    }
}

proguard-rules.pro

-keep class com.xyz.demo.** {*;}

也试过了 -keep class com.xyz.demo.OptionalDependencies {*;}

e:/Users/sample/src/main/java/com/xyz/demo/ui/StartActivity.kt: (527, 42): Unresolved reference: OptionalDependencies

如果关掉程序,它就可以正常工作。