需要排除Gson上的序列化/反序列化类。对于包含类的包，如下所示

# Application classes that will be serialized/deserialized over Gson
-keep class com.myapplication.model.api.** { *; }

还要加上这个

# Gson uses generic type information stored in a class file when working with
# fields. Proguard removes such information by default, keep it.
-keepattributes Signature

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