fix(@langchain/google-genai): safe access around custom content parts (#9584)

Co-authored-by: Hunter Lovell <[email protected]>

Author: encodedz

.changeset/good-pillows-reflect.md

@@ -0,0 +1,5 @@
+---
+"@langchain/google-genai": patch
+---
+
+safe access around custom content parts

libs/providers/langchain-google-genai/src/utils/common.ts

@@ -527,7 +527,7 @@ export function mapGenerateContentResultToChatResult(
   }
   const [candidate] = response.candidates;
   const { content: candidateContent, ...generationInfo } = candidate;
-  const functionCalls = candidateContent.parts.reduce((acc, p) => {
+  const functionCalls = candidateContent.parts?.reduce((acc, p) => {
     if ("functionCall" in p && p.functionCall) {
       acc.push({
         ...p,
@@ -655,7 +655,7 @@ export function convertResponseContentToChatGenerationChunk(
   }
   const [candidate] = response.candidates;
   const { content: candidateContent, ...generationInfo } = candidate;
-  const functionCalls = candidateContent.parts.reduce((acc, p) => {
+  const functionCalls = candidateContent.parts?.reduce((acc, p) => {
     if ("functionCall" in p && p.functionCall) {
       acc.push({
         ...p,