diff --git a/package.json b/package.json
index 3939b6a..99b7a12 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@samchon/openapi",
-  "version": "2.0.0-dev.20241129",
+  "version": "2.0.0-dev.20241129-4",
   "description": "OpenAPI definitions and converters for 'typia' and 'nestia'.",
   "main": "./lib/index.js",
   "module": "./lib/index.mjs",
diff --git a/src/converters/ChatGptConverter.ts b/src/converters/ChatGptConverter.ts
index 7ae4417..bcaf397 100644
--- a/src/converters/ChatGptConverter.ts
+++ b/src/converters/ChatGptConverter.ts
@@ -21,6 +21,7 @@ export namespace ChatGptConverter {
           reference: props.config.reference,
           constraint: false,
         },
+        validate: validate(props.errors),
       });
     if (params === null) return null;
     for (const key of Object.keys(params.$defs))
@@ -44,19 +45,7 @@ export namespace ChatGptConverter {
         reference: props.config.reference,
         constraint: false,
       },
-      validate: (schema, accessor) => {
-        if (
-          OpenApiTypeChecker.isObject(schema) &&
-          !!schema.additionalProperties
-        ) {
-          if (props.errors)
-            props.errors.push(
-              `${accessor}.additionalProperties: ChatGPT does not allow additionalProperties, the dynamic key typed object.`,
-            );
-          return false;
-        }
-        return true;
-      },
+      validate: validate(props.errors),
     });
     if (schema === null) return null;
     for (const key of Object.keys(props.$defs))
@@ -65,6 +54,22 @@ export namespace ChatGptConverter {
     return transform(schema);
   };
 
+  const validate =
+    (errors: string[] | undefined) =>
+    (schema: OpenApi.IJsonSchema, accessor: string): boolean => {
+      if (
+        OpenApiTypeChecker.isObject(schema) &&
+        !!schema.additionalProperties
+      ) {
+        if (errors)
+          errors.push(
+            `${accessor}.additionalProperties: ChatGPT does not allow additionalProperties, the dynamic key typed object.`,
+          );
+        return false;
+      }
+      return true;
+    };
+
   const transform = (schema: ILlmSchemaV3_1): IChatGptSchema => {
     const union: Array<IChatGptSchema> = [];
     const attribute: IChatGptSchema.__IAttribute = {
diff --git a/src/converters/GeminiConverter.ts b/src/converters/GeminiConverter.ts
index bd775b8..be6f24f 100644
--- a/src/converters/GeminiConverter.ts
+++ b/src/converters/GeminiConverter.ts
@@ -2,6 +2,7 @@ import { OpenApi } from "../OpenApi";
 import { IGeminiSchema } from "../structures/IGeminiSchema";
 import { ILlmSchemaV3 } from "../structures/ILlmSchemaV3";
 import { LlmTypeCheckerV3 } from "../utils/LlmTypeCheckerV3";
+import { MapUtil } from "../utils/MapUtil";
 import { OpenApiTypeChecker } from "../utils/OpenApiTypeChecker";
 import { LlmConverterV3 } from "./LlmConverterV3";
 import { LlmParametersFinder } from "./LlmParametersFinder";
@@ -47,6 +48,40 @@ export namespace GeminiConverter {
             return false;
           }
         } else if (OpenApiTypeChecker.isOneOf(next)) {
+          // NULLABLE CASE
+          const notNull = next.oneOf.filter(
+            (v) => OpenApiTypeChecker.isNull(v) === false,
+          );
+          if (notNull.length < 2) return true;
+
+          // ENUM CASE
+          const constants: OpenApi.IJsonSchema.IConstant[] = notNull.filter(
+            (v) => OpenApiTypeChecker.isConstant(v),
+          );
+          const dict: Map<"boolean" | "number" | "string", any> = new Map();
+          for (const v of constants)
+            MapUtil.take(dict)(typeof v.const as "number")(() => []).push(
+              v.const,
+            );
+          if (dict.size === 1) {
+            if (notNull.length === constants.length) return true;
+            const atomic = notNull.filter(
+              (v) =>
+                OpenApiTypeChecker.isBoolean(v) ||
+                OpenApiTypeChecker.isInteger(v) ||
+                OpenApiTypeChecker.isNumber(v) ||
+                OpenApiTypeChecker.isString(v),
+            );
+            if (atomic.length === 1)
+              if (atomic[0].type === "integer")
+                return (
+                  dict.has("number") &&
+                  dict.get("number")!.every((v: number) => Number.isInteger(v))
+                );
+              else return dict.has(atomic[0].type);
+          }
+
+          // REAL ONE-OF TYPE
           if (props.errors)
             props.errors.push(`${accessor}: Gemini does not allow union type.`);
           return false;
diff --git a/src/converters/LlmConverterV3_1.ts b/src/converters/LlmConverterV3_1.ts
index 8788e0c..0e24c1e 100644
--- a/src/converters/LlmConverterV3_1.ts
+++ b/src/converters/LlmConverterV3_1.ts
@@ -13,6 +13,7 @@ export namespace LlmConverterV3_1 {
     schema: OpenApi.IJsonSchema.IObject | OpenApi.IJsonSchema.IReference;
     errors?: string[];
     accessor?: string;
+    validate?: (input: OpenApi.IJsonSchema, accessor: string) => boolean;
   }): ILlmSchemaV3_1.IParameters | null => {
     const entity: OpenApi.IJsonSchema.IObject | null =
       LlmParametersFinder.find(props);
diff --git a/test/features/llm/gemini/test_gemini_schema_enum.ts b/test/features/llm/gemini/test_gemini_schema_enum.ts
new file mode 100644
index 0000000..5abf2c0
--- /dev/null
+++ b/test/features/llm/gemini/test_gemini_schema_enum.ts
@@ -0,0 +1,25 @@
+import { TestValidator } from "@nestia/e2e";
+import { LlmSchemaConverter } from "@samchon/openapi/lib/converters/LlmSchemaConverter";
+import typia, { IJsonSchemaCollection, tags } from "typia";
+
+export const test_gemini_schema_enum = (): void => {
+  const collection: IJsonSchemaCollection =
+    typia.json.schemas<
+      [
+        0 | 1 | 2,
+        (number & {}) | 1.2 | 2.3 | 3.4,
+        (number & tags.Type<"int32">) | 1 | 2 | 3,
+        "one" | "two" | "three",
+      ]
+    >();
+  for (const schema of collection.schemas) {
+    const errors: string[] = [];
+    const gemini = LlmSchemaConverter.schema("gemini")({
+      config: LlmSchemaConverter.defaultConfig("gemini"),
+      components: collection.components,
+      schema,
+      errors,
+    });
+    TestValidator.equals("success")(!!gemini)(true);
+  }
+};
diff --git a/test/features/llm/gemini/test_gemini_schema_nullable.ts b/test/features/llm/gemini/test_gemini_schema_nullable.ts
new file mode 100644
index 0000000..1d64807
--- /dev/null
+++ b/test/features/llm/gemini/test_gemini_schema_nullable.ts
@@ -0,0 +1,46 @@
+import { TestValidator } from "@nestia/e2e";
+import { LlmSchemaConverter } from "@samchon/openapi/lib/converters/LlmSchemaConverter";
+import typia, { IJsonSchemaCollection } from "typia";
+
+export const test_gemini_schema_nullable = (): void => {
+  const collection: IJsonSchemaCollection = typia.json.schemas<
+    [
+      0 | 1 | 2 | 3 | null,
+      (number & {}) | 1.2 | 2.3 | 3.4 | null,
+      {
+        id: string | null;
+        value: number;
+      } | null,
+      Array<number> | null,
+      Array<{
+        nested: Array<{
+          id: string | null;
+        }>;
+        nullable: Array<string | null>;
+      }>,
+      {
+        first: ToJsonNull;
+        second: ToJsonNull | null;
+      },
+      {
+        first: ToJsonNull | null;
+        second: ToJsonNull | null;
+        third?: ToJsonNull | null;
+      },
+    ]
+  >();
+  for (const schema of collection.schemas) {
+    const errors: string[] = [];
+    const gemini = LlmSchemaConverter.schema("gemini")({
+      config: LlmSchemaConverter.defaultConfig("gemini"),
+      components: collection.components,
+      schema,
+      errors,
+    });
+    TestValidator.equals("success")(!!gemini)(true);
+  }
+};
+
+interface ToJsonNull {
+  toJSON: () => null;
+}