[AI] Correctly handle empty candidates in the accessors

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()
         }
       }
     }