title: What does `moshi` in the adapter-constructor generated by codegen mean?
body: <p>I'm a newbee in kotlin-android development.</p>
  
  <p>I want to parse a JSON like</p>
  
  <pre><code>{
    "name": "This is my name",
  }
  </code></pre>
  
  <p>to a <code>Foo</code> class defined as</p>
  
  <p>Foo.kt</p>
  
  <pre><code>@JsonClass(generateAdapter = true)
  data class Foo(val name: String)
  </code></pre>
  
  <p>This <code>Foo</code> class file generates a code by codegen as follows.</p>
  
  <p>FooJsonAdapter.kt (generated by codegen)</p>
  
  <pre><code>class FooJsonAdapter(moshi: Moshi) : JsonAdapter&lt;Foo&gt;() {
      private val options: JsonReader.Options
  
      private val stringAdapter: JsonAdapter&lt;String&gt;
  
      override fun toString(): String
  
      override fun fromJson(reader: JsonReader): Foo 
  
      override fun toJson(writer: JsonWriter, value: Foo?) 
  }
  </code></pre>
  
  <p>The <code>FooJsonAdapter</code> class's constructor specifies <code>Moshi</code> object, and here is my question.
  What kind of <code>Moshi</code> object should be passed to the constructor? I tried the following, but this does not work.</p>
  
  <p>MainActivity.kt</p>
  
  <pre><code>Moshi.Builder().add(
      FooJsonAdapter(
          Moshi.Builder().build()
      )
  ).build()
  </code></pre>
  
  <p>Error message</p>
  
  <pre><code>E/AndroidRuntime: FATAL EXCEPTION: main
      Process: com.example.hoge, PID: 31816
      java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.hoge/com.example.hoge.MainActivity}: java.lang.IllegalArgumentException: Expected at least one @ToJson or @FromJson method on com.example.hoge.FooJsonAdapter
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3260)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3396)
          at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
          at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
          at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
          at android.os.Handler.dispatchMessage(Handler.java:107)
          at android.os.Looper.loop(Looper.java:214)
          at android.app.ActivityThread.main(ActivityThread.java:7319)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:934)
       Caused by: java.lang.IllegalArgumentException: Expected at least one @ToJson or @FromJson method on com.example.hoge.FooJsonAdapter
          at com.squareup.moshi.AdapterMethodsFactory.get(AdapterMethodsFactory.java:137)
          at com.squareup.moshi.Moshi$Builder.add(Moshi.java:237)
          at com.example.hoge.MainActivity.onCreate(MainActivity.kt:14)
          at android.app.Activity.performCreate(Activity.java:7783)
          at android.app.Activity.performCreate(Activity.java:7772)
          at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3235)
          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3396) 
          at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
          at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
          at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009) 
          at android.os.Handler.dispatchMessage(Handler.java:107) 
          at android.os.Looper.loop(Looper.java:214) 
          at android.app.ActivityThread.main(ActivityThread.java:7319) 
          at java.lang.reflect.Method.invoke(Native Method) 
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:934) 
  </code></pre>
  
  <p>What should I do? Thx!</p>