chore: Support _self key in request object config

PiperOrigin-RevId: 804484893

Author: matthew29tang

src/main/java/com/google/genai/Common.java

@@ -102,8 +102,13 @@ static void setValueByPath(ObjectNode jsonObject, String[] path, Object value) {
     }
 
     String keyToSet = path[path.length - 1];
-    JsonNode valueNode = JsonSerializable.toJsonNode(value);
-    Transformers.updateJsonNode(currentObject, keyToSet, valueNode);
+    if (keyToSet.equals("_self") && value instanceof ObjectNode) {
+      ObjectNode sourceNode = (ObjectNode) value;
+      currentObject.setAll(sourceNode);
+    } else {
+      JsonNode valueNode = JsonSerializable.toJsonNode(value);
+      Transformers.updateJsonNode(currentObject, keyToSet, valueNode);
+    }
   }
 
   /**

src/test/java/com/google/genai/CommonTest.java

@@ -72,6 +72,19 @@ public void testSetValueByPath_firstArrayElement() {
     assertEquals("v4", data.get("a").get("b").get(0).get("c").asText());
   }
 
+  @Test
+  public void testSetValueByPath_selfKey() {
+    ObjectNode data = JsonSerializable.objectMapper.createObjectNode();
+    data.putObject("a").putObject("b");
+    ObjectNode value = JsonSerializable.objectMapper.createObjectNode();
+    value.put("c", "v");
+    Common.setValueByPath(data, new String[] {"_self"}, value);
+
+    // expected output: {a: {b: {}}, c: "v"}
+    assertEquals("", data.get("a").get("b").asText());
+    assertEquals("v", data.get("c").asText());
+  }
+
   @Test
   public void testGetValueByPath_simpleObject() {
     ObjectNode data = JsonSerializable.objectMapper.createObjectNode();