GSON is not serializing data when in library module

Question

I wrote a small library module, and I'm trying to consume some JSON data. However, GSON is not serializing the data. It's not throwing any errors. Everything is just null. Further, if I move the same code out of the library and into my app (in this case I just put it in App.kt) then it works.

Why wouldn't GSON serialize when in a Library Module? Is there something else I need to do?

---

In the library module

data class MyMessage(@SerializedName("message") val message: String?)

object MessageCenter {
    
    private const val TAG = "MessageCenter"

    init {
        val json = "{\"message\":\"A custom message\"}"
        Log.d(TAG,  "JSON RAW $json")

        val mm: MyMessage = Gson().fromJson(json, MyMessage::class.java)
        Log.d(TAG,  "MyMessage: ${mm.message}")
    }

    fun start(){
        Log.i(TAG,  "Message Center Started")
    }

}

build.gradle

dependencies {
    implementation 'com.google.code.gson:gson:2.8.6'
}

In my App

class App : Application() {
    override fun onCreate() {
        super.onCreate()
        MessageCenter.start()
    }
}

build.gradle The App also needs Gson for other libraries. So it is also found in the app's module build.gradle.

dependencies {
    implementation 'com.google.code.gson:gson:2.8.6'
    implementation project(':messagecenter')
}

D/MessageCenter: JSON RAW {"message":"A custom message"}
D/MessageCenter: MyMessage: null
I/MessageCenter: Message Center Started

---

If I bring the code and data class out of the library and into my main app then GSON works:

data class MyMessage(@SerializedName("message") val message: String?)

class App : Application() {

    override fun onCreate() {
        super.onCreate()
        MessageCenter.start()
        val json = "{\"message\":\"A custom message\"}"
        Log.d("App.kt",  "JSON RAW $json")

        val mm: MyMessage = Gson().fromJson(json, MyMessage::class.java)
        Log.d("App.kt",  "MyMessage: ${mm.message}")
    }
}

D/MessageCenter: JSON RAW {"message":"A custom message"}
D/MessageCenter: MyMessage: null
I/MessageCenter: Message Center Started

D/App.kt: JSON RAW {"message":"A custom message"}
D/App.kt: MyMessage: A custom message

---

Here is my progaurd-rules for my library:

 -keepattributes Signature

 # For using GSON @Expose annotation
 -keepattributes *Annotation*

 # Gson specific classes
 -dontwarn sun.misc.**
 #-keep class com.google.gson.stream.** { *; }

 # Application classes that will be serialized/deserialized over Gson
 -keep class com.mycompany.messagecenter.data.* { <fields>; }

 # Prevent proguard from stripping interface information from TypeAdapter, TypeAdapterFactory,
 # JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
 -keep class * implements com.google.gson.TypeAdapter
 -keep class * implements com.google.gson.TypeAdapterFactory
 -keep class * implements com.google.gson.JsonSerializer
 -keep class * implements com.google.gson.JsonDeserializer

 # Prevent R8 from leaving Data object members always null
 -keepclassmembers,allowobfuscation class * {
   @com.google.gson.annotations.SerializedName <fields>;
 }