这到底是什么错啊，有的说retrofit2版本问题，我升级到2.9了还是会这样，我在AS编译到手机不会出现闪退，如果打包APK后请求网络接口就会闪退报错，如截图的日志，
java.lang.IllegalArgumentException: Unable to create call adapter for class t8.b
for method a.a
at s9.k.r(Unknown Source:39)
at db.s.b(Unknown Source:2696)
at db.u0.b(Unknown Source:30)
at db.t0.invoke(Unknown Source:44)
at java.lang.reflect.Proxy.invoke(Proxy.java:1006)
at $Proxy3.a(Unknown Source)
at l6.a.m(Unknown Source:18)
at d6.k.onClick(Unknown Source:155)
at android.view.View.performClick(View.java:7616)
at android.view.View.performClickInternal(View.java:7590)
at android.view.View.access$3800(View.java:868)
at android.view.View$PerformClick.run(View.java:29449)
at android.os.Handler.handleCallback(Handler.java:955)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loopOnce(Looper.java:206)
at android.os.Looper.loop(Looper.java:296)
at android.app.ActivityThread.main(ActivityThread.java:9000)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:569)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:976)
Caused by: java.lang.IllegalStateException: Observable return type must be parameterized as Observable<Foo> or Observable<? extends Foo>
at eb.h.a(Unknown Source:114)
at db.u0.a(Unknown Source:32)
at db.s.b(Unknown Source:2534)
at db.u0.b(Unknown Source:30)
at db.t0.invoke(Unknown Source:44)
at java.lang.reflect.Proxy.invoke(Proxy.java:1006)
at $Proxy3.a(Unknown Source)
at l6.a.m(Unknown Source:18)
at d6.k.onClick(Unknown Source:155)
at android.view.View.performClick(View.java:7616)
at android.view.View.performClickInternal(View.java:7590)
at android.view.View.access$3800(View.java:868)
at android.view.View$PerformClick.run(View.java:29449)
at android.os.Handler.handleCallback(Handler.java:955)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loopOnce(Looper.java:206)
at android.os.Looper.loop(Looper.java:296)
at android.app.ActivityThread.main(ActivityThread.java:9000)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:569)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:976)
