[AI] Correctly handle empty candidates in the accessors (#7270)

Before, if a response had no candidates, accessors would throw an
exception when used instead of handle the case elegantly. Now they
either return an empty list, for collections, or null, for string.

The test file is added in
FirebaseExtended/vertexai-sdk-test-data#48

Author: rlazo

firebase-ai/CHANGELOG.md

@@ -1,12 +1,14 @@
 # Unreleased
+* [fixed] Fixed an issue causing the accessor methods in `GenerateContentResponse` to throw an exception
+  when the response contained no candidates.
 * [changed] Added better description for requests which fail due to the Gemini API not being
   configured.
 * [changed] Added a `dilation` parameter to `ImagenMaskReference.generateMaskAndPadForOutpainting`
   (#7260)
 
 # 17.1.0
 =======
-* [feature] added support for Imagen Editing, including inpainting, outpainting, control, style 
+* [feature] added support for Imagen Editing, including inpainting, outpainting, control, style
   transfer, and subject references (#7075)
 * [feature] **Preview:** Added support for bidirectional streaming in Gemini Developer Api
 
@@ -51,4 +53,3 @@
 
  Note: This feature is in Public Preview, which means that it is not subject to any SLA or
  deprecation policy and could change in backwards-incompatible ways.
-

firebase-ai/src/main/kotlin/com/google/firebase/ai/type/GenerateContentResponse.kt

@@ -32,28 +32,42 @@ public class GenerateContentResponse(
   public val usageMetadata: UsageMetadata?,
 ) {
   /**
-   * Convenience field representing all the text parts in the response as a single string, if they
-   * exists.
+   * Convenience field representing all the text parts in the response as a single string.
+   *
+   * The value is null if the response contains no [candidates].
    */
   public val text: String? by lazy {
-    candidates.first().content.parts.filterIsInstance<TextPart>().joinToString(" ") { it.text }
+    candidates.firstOrNull()?.content?.parts?.filterIsInstance<TextPart>()?.joinToString(" ") {
+      it.text
+    }
   }
 
-  /** Convenience field to list all the [FunctionCallPart]s in the response, if they exist. */
+  /**
+   * Convenience field to list all the [FunctionCallPart]s in the response.
+   *
+   * The value is an empty list if the response contains no [candidates].
+   */
   public val functionCalls: List<FunctionCallPart> by lazy {
-    candidates.first().content.parts.filterIsInstance<FunctionCallPart>()
+    candidates.firstOrNull()?.content?.parts?.filterIsInstance<FunctionCallPart>().orEmpty()
   }
 
   /**
    * Convenience field representing all the [InlineDataPart]s in the first candidate, if they exist.
    *
    * This also includes any [ImagePart], but they will be represented as [InlineDataPart] instead.
+   *
+   * The value is an empty list if the response contains no [candidates].
    */
   public val inlineDataParts: List<InlineDataPart> by lazy {
-    candidates.first().content.parts.let { parts ->
-      parts.filterIsInstance<ImagePart>().map { it.toInlineDataPart() } +
-        parts.filterIsInstance<InlineDataPart>()
-    }
+    candidates
+      .firstOrNull()
+      ?.content
+      ?.parts
+      ?.let { parts ->
+        parts.filterIsInstance<ImagePart>().map { it.toInlineDataPart() } +
+          parts.filterIsInstance<InlineDataPart>()
+      }
+      .orEmpty()
   }
 
   @Serializable

firebase-ai/src/test/java/com/google/firebase/ai/DevAPIUnarySnapshotTests.kt

@@ -22,12 +22,12 @@ import com.google.firebase.ai.type.ResponseStoppedException
 import com.google.firebase.ai.type.ServerException
 import com.google.firebase.ai.util.goldenDevAPIUnaryFile
 import io.kotest.assertions.throwables.shouldThrow
+import io.kotest.matchers.collections.shouldBeEmpty
 import io.kotest.matchers.collections.shouldNotBeEmpty
 import io.kotest.matchers.nulls.shouldBeNull
 import io.kotest.matchers.nulls.shouldNotBeNull
 import io.kotest.matchers.should
 import io.kotest.matchers.shouldBe
-import io.kotest.matchers.shouldNotBe
 import io.ktor.http.HttpStatusCode
 import kotlin.time.Duration.Companion.seconds
 import kotlinx.coroutines.withTimeout
@@ -42,9 +42,24 @@ internal class DevAPIUnarySnapshotTests {
       withTimeout(testTimeout) {
         val response = model.generateContent("prompt")
 
-        response.candidates.isEmpty() shouldBe false
+        response.candidates.shouldNotBeEmpty()
         response.candidates.first().finishReason shouldBe FinishReason.STOP
-        response.candidates.first().content.parts.isEmpty() shouldBe false
+        response.candidates.first().content.parts.shouldNotBeEmpty()
+      }
+    }
+
+  @Test
+  fun `only prompt feedback reply`() =
+    goldenDevAPIUnaryFile("unary-failure-only-prompt-feedback.json") {
+      withTimeout(testTimeout) {
+        val response = model.generateContent("prompt")
+
+        response.candidates.shouldBeEmpty()
+
+        // Check response from accessors
+        response.text.shouldBeNull()
+        response.functionCalls.shouldBeEmpty()
+        response.inlineDataParts.shouldBeEmpty()
       }
     }
 
@@ -54,9 +69,9 @@ internal class DevAPIUnarySnapshotTests {
       withTimeout(testTimeout) {
         val response = model.generateContent("prompt")
 
-        response.candidates.isEmpty() shouldBe false
+        response.candidates.shouldNotBeEmpty()
         response.candidates.first().finishReason shouldBe FinishReason.STOP
-        response.candidates.first().content.parts.isEmpty() shouldBe false
+        response.candidates.first().content.parts.shouldNotBeEmpty()
       }
     }
 
@@ -66,11 +81,11 @@ internal class DevAPIUnarySnapshotTests {
       withTimeout(testTimeout) {
         val response = model.generateContent("prompt")
 
-        response.candidates.isEmpty() shouldBe false
+        response.candidates.shouldNotBeEmpty()
         response.candidates.first().citationMetadata?.citations?.size shouldBe 4
         response.candidates.first().citationMetadata?.citations?.forEach {
-          it.startIndex shouldNotBe null
-          it.endIndex shouldNotBe null
+          it.startIndex.shouldNotBeNull()
+          it.endIndex.shouldNotBeNull()
         }
       }
     }