proto convertion support nullvalue (opensearch-project#189)

Add NULLVALUE template

reformat

Signed-off-by: xil <fridalu66@gmail.com>

Author: lucy66hw

CHANGELOG.md

@@ -5,6 +5,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ## [Unreleased]
 ### Added
 - Publish opensearch-protos python package to PyPi. ([#183](https://github.com/opensearch-project/opensearch-protobufs/pull/183))
+- Proto Convertion tooling support null value ([#189](https://github.com/opensearch-project/opensearch-protobufs/pull/189))
 
 ### Changed
 - update `score` protobuf type ([#179](https://github.com/opensearch-project/opensearch-protobufs/pull/179))

tools/proto-convert/src/SchemaModifier.ts

@@ -20,12 +20,14 @@ export class SchemaModifier {
             onSchemaProperty: (schema) => {
                 this.deduplicateEnumValue(schema)
                 this.handleAdditionalPropertiesUndefined(schema)
+                this.convertNullTypeToNullValue(schema)
                 this.collapseOrMergeOneOfArray(schema)
             },
             onSchema: (schema, schemaName) => {
                 if (!schema || isReferenceObject(schema)) return;
                 this.deduplicateEnumValue(schema)
                 this.handleAdditionalPropertiesUndefined(schema)
+                this.convertNullTypeToNullValue(schema)
                 this.handleOneOfConst(schema, schemaName)
                 this.collapseOrMergeOneOfArray(schema)
                 this.collapseOneOfObjectPropContainsTitleSchema(schema)
@@ -333,4 +335,11 @@ export class SchemaModifier {
 
         schema.enum = Array.from(enumSet)
     }
+
+    // Converts type: "null" to type: NullValue for protobuf compatibility
+    convertNullTypeToNullValue(schema: OpenAPIV3.SchemaObject): void {
+        if ((schema.type as any) === 'null') {
+            (schema as any).type = 'NullValue';
+        }
+    }
 }

tools/proto-convert/src/config/protobuf-schema-template/custom_message.mustache

@@ -30,3 +30,8 @@ message GeneralNumber {
     double double_value = 4;
   }
 }
+
+enum NullValue {
+  NULL_VALUE_UNSPECIFIED = 0;
+  NULL_VALUE_NULL = 1;
+}