Fix direct serialization of primitive types in DEFAULT_JSONP_MAPPER

Signed-off-by: Thomas Farr <tsfarr@amazon.com>

Author: Xtansia

java-client/src/main/java/org/opensearch/client/json/JsonpUtils.java

@@ -43,6 +43,8 @@
 import jakarta.json.stream.JsonParser.Event;
 import jakarta.json.stream.JsonParsingException;
 import java.io.StringReader;
+import java.math.BigDecimal;
+import java.math.BigInteger;
 import java.util.AbstractMap;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -78,11 +80,31 @@ public JsonProvider jsonProvider() {
         public <T> void serialize(T value, JsonGenerator generator) {
             if (value instanceof JsonpSerializable) {
                 ((JsonpSerializable) value).serialize(generator, this);
-                return;
+            } else if (value instanceof JsonValue) {
+                generator.write((JsonValue) value);
+            } else if (value instanceof String) {
+                generator.write((String) value);
+            } else if (value instanceof BigDecimal) {
+                generator.write((BigDecimal) value);
+            } else if (value instanceof BigInteger) {
+                generator.write((BigInteger) value);
+            } else if (value instanceof Short) {
+                generator.write((Short) value);
+            } else if (value instanceof Integer) {
+                generator.write((Integer) value);
+            } else if (value instanceof Long) {
+                generator.write((Long) value);
+            } else if (value instanceof Float) {
+                generator.write((Float) value);
+            } else if (value instanceof Double) {
+                generator.write((Double) value);
+            } else if (value instanceof Boolean) {
+                generator.write((Boolean) value);
+            } else {
+                throw new JsonException(
+                    "Cannot find a serializer for type " + value.getClass().getName() + ". Consider using a full-featured JsonpMapper."
+                );
             }
-            throw new JsonException(
-                "Cannot find a serializer for type " + value.getClass().getName() + ". Consider using a full-featured JsonpMapper."
-            );
         }
 
         @Override

java-client/src/test/java/org/opensearch/client/opensearch/core/IndexRequestTest.java

@@ -28,4 +28,10 @@ static class MyDoc {
             this.key = key;
         }
     }
+
+    @Test
+    public void indexRequestToJson() {
+        IndexRequest<Object> indexRequest = IndexRequest.of(i -> i.index("index").document("document"));
+        assertNotNull(indexRequest.toJsonString());
+    }
 }