fix: serialize Gson elements in additional data

components/serialization/json/src/main/java/com/microsoft/kiota/serialization/JsonSerializationWriter.java

@@ -1,6 +1,7 @@
 package com.microsoft.kiota.serialization;
 
 import com.google.gson.Gson;
+import com.google.gson.JsonElement;
 import com.google.gson.stream.JsonWriter;
 import com.microsoft.kiota.PeriodAndDuration;
 
@@ -474,12 +475,22 @@ private void writeNonParsableObject(@Nullable final String key, @Nullable final
         }
     }
 
+    private void writeJsonElement(@Nullable final String key, @Nonnull final JsonElement value) {
+        try {
+            if (key != null && !key.isEmpty()) writer.name(key);
+            gson.getAdapter(JsonElement.class).write(writer, value);
+        } catch (IOException ex) {
+            throw new RuntimeException("could not serialize value", ex);
+        }
+    }
+
     private void writeAnyValue(@Nullable final String key, @Nullable final Object value) {
         if (value == null) {
             this.writeNullValue(key);
         } else {
             final Class<?> valueClass = value.getClass();
-            if (valueClass.equals(String.class)) this.writeStringValue(key, (String) value);
+            if (value instanceof JsonElement) this.writeJsonElement(key, (JsonElement) value);
+            else if (valueClass.equals(String.class)) this.writeStringValue(key, (String) value);
             else if (valueClass.equals(Boolean.class)) this.writeBooleanValue(key, (Boolean) value);
             else if (valueClass.equals(Byte.class)) this.writeByteValue(key, (Byte) value);
             else if (valueClass.equals(Short.class)) this.writeShortValue(key, (Short) value);

components/serialization/json/src/test/java/com/microsoft/kiota/serialization/JsonSerializationWriterTests.java

@@ -4,13 +4,16 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 
+import com.google.gson.JsonParser;
 import com.microsoft.kiota.Compatibility;
 import com.microsoft.kiota.PeriodAndDuration;
 import com.microsoft.kiota.serialization.mocks.MyEnum;
 import com.microsoft.kiota.serialization.mocks.TestEntity;
 import com.microsoft.kiota.serialization.mocks.UntypedTestEntity;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 import java.io.IOException;
 import java.math.BigDecimal;
@@ -26,6 +29,31 @@
 import java.util.UUID;
 
 class JsonSerializationWriterTests {
+    @ParameterizedTest
+    @ValueSource(
+            strings = {
+                "{\"@odata.type\":\"#CustomSecurityAttributeValue\",\"ids\":[\"123\",\"321\"],\"nested\":{\"nil\":null}}",
+                "[1,false,null,{\"name\":\"test\"}]",
+                "\"quoted \\\" text\"",
+                "false",
+                "123456789012345678901234567890",
+                "null",
+                "{}",
+                "[]"
+            })
+    void serializesJsonElementsInAdditionalData(String json) throws IOException {
+        var entity = new TestEntity();
+        entity.getAdditionalData().put("extra", JsonParser.parseString(json));
+        try (var serializer = new JsonSerializationWriter()) {
+            serializer.writeObjectValue(null, entity);
+            var actual =
+                    new String(
+                            Compatibility.readAllBytes(serializer.getSerializedContent()), "UTF-8");
+            assertEquals(
+                    JsonParser.parseString("{\"extra\":" + json + "}"),
+                    JsonParser.parseString(actual));
+        }
+    }
 
     @Test
     void writesSampleObjectValueWithPrimitivesInAdditionalData() throws IOException {