Excludes the empty string properties from request body. Simply add dd this gson object to your retrofit client.

GsonTypeAdapter.kt

@Singleton
@Provides
fun provideGson() : Gson = GsonBuilder().registerTypeAdapter(String::class.java ,object : TypeAdapter<String>() {
    override fun write(out: JsonWriter?, value: String?) {
        if(value.isNullOrBlank()) {
            out?.nullValue()
            return
        }
        out?.value(value)
    }

    override fun read(inn: JsonReader?): String? {
        return inn?.nextString()
    }
}).create()