add throwable type adapter

remote-robot/src/main/kotlin/com/intellij/remoterobot/RemoteRobot.kt

@@ -2,6 +2,7 @@
 
 package com.intellij.remoterobot
 
+import com.google.gson.GsonBuilder
 import com.intellij.remoterobot.client.IdeRobotApi
 import com.intellij.remoterobot.client.IdeRobotClient
 import com.intellij.remoterobot.data.RemoteComponent
@@ -14,6 +15,7 @@ import com.intellij.remoterobot.fixtures.Fixture
 import com.intellij.remoterobot.search.Finder
 import com.intellij.remoterobot.search.locators.Locator
 import com.intellij.remoterobot.utils.DefaultHttpClient
+import com.intellij.remoterobot.utils.ThrowableTypeAdapter
 import com.intellij.remoterobot.utils.waitFor
 import okhttp3.OkHttpClient
 import org.intellij.lang.annotations.Language
@@ -28,15 +30,19 @@ import javax.imageio.ImageIO
 @DslMarker
 annotation class RemoteCommand
 
-
 class RemoteRobot @JvmOverloads constructor(
     robotServerUrl: String,
     okHttpClient: OkHttpClient = DefaultHttpClient.client,
     secret: String? = null
 ) : SearchContext, JavaScriptApi, LambdaApi {
+
+    private val gson = GsonBuilder()
+        .registerTypeAdapter(Throwable::class.java, ThrowableTypeAdapter)
+        .create()
+
     override val ideRobotClient = IdeRobotClient(
         Retrofit.Builder().baseUrl(robotServerUrl)
-            .addConverterFactory(GsonConverterFactory.create())
+            .addConverterFactory(GsonConverterFactory.create(gson))
             .client(okHttpClient)
             .build()
             .create(IdeRobotApi::class.java)

remote-robot/src/main/kotlin/com/intellij/remoterobot/utils/ThrowableTypeAdapter.kt

@@ -0,0 +1,36 @@
+package com.intellij.remoterobot.utils
+
+import com.google.gson.TypeAdapter
+import com.google.gson.stream.JsonReader
+import com.google.gson.stream.JsonWriter
+
+object ThrowableTypeAdapter : TypeAdapter<Throwable>() {
+
+    override fun write(writer: JsonWriter, value: Throwable?) {
+        if (value == null) {
+            writer.nullValue()
+            return
+        }
+        writer.beginObject()
+
+        // Include exception type name to give more context; for example, NullPointerException might
+        // not have a message
+        writer.name("type")
+        writer.value(value::class.java.getSimpleName())
+
+        writer.name("message")
+        writer.value(value.message)
+
+        val cause = value.cause
+        if (cause != null) {
+            writer.name("cause")
+            write(writer, cause)
+        }
+
+        writer.endObject()
+    }
+
+    override fun read(reader: JsonReader): Throwable {
+        throw UnsupportedOperationException()
+    }
+}