diff --git a/webview_rpc_runtime_library/CHANGELOG.md b/webview_rpc_runtime_library/CHANGELOG.md
index 93fa131..ee4c17a 100644
--- a/webview_rpc_runtime_library/CHANGELOG.md
+++ b/webview_rpc_runtime_library/CHANGELOG.md
@@ -5,7 +5,24 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [1.0.1] - 2025-06-23
+## [1.0.4] - 2025-06-24
+
+### Fixed
+- Fixed null handling issue in RPC envelope encoding
+  - WebViewRpcClient and WebViewRpcServer were explicitly setting `error` field to `null`
+  - This caused `Cannot read properties of null (reading 'length')` error
+  - Now follows Proto3 spec: optional fields are omitted instead of set to null
+  - Proto3 string fields default to empty string automatically when not set
+
+## [1.0.3] - 2025-06-23
+
+### Fixed
+- Fixed npm package build issue where wrong function names were in the published package
+  - The source code used `base64ToUint8Array` and `uint8ArrayToBase64`
+  - But the published npm package incorrectly had `base64ToBytes` and `base64FromBytes`
+  - This caused import errors when using the package
+
+## [1.0.2] - 2025-06-23
 
 ### Changed
 - **BREAKING**: Complete redesign for async-only architecture
diff --git a/webview_rpc_runtime_library/package-lock.json b/webview_rpc_runtime_library/package-lock.json
index c6ccfdc..f02b780 100644
--- a/webview_rpc_runtime_library/package-lock.json
+++ b/webview_rpc_runtime_library/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "app-webview-rpc",
-  "version": "1.0.0",
+  "version": "1.0.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "app-webview-rpc",
-      "version": "1.0.0",
+      "version": "1.0.1",
       "license": "MIT",
       "devDependencies": {
         "rimraf": "^5.0.0",
diff --git a/webview_rpc_runtime_library/package.json b/webview_rpc_runtime_library/package.json
index 0984496..7ec701f 100644
--- a/webview_rpc_runtime_library/package.json
+++ b/webview_rpc_runtime_library/package.json
@@ -1,6 +1,6 @@
 {
   "name": "app-webview-rpc",
-  "version": "1.0.1",
+  "version": "1.0.4",
   "type": "module",
   "description": "WebView RPC provides an abstraction layer that allows communication between the App (e.g. Unity C#) and WebView (HTML, JS) using protobuf, similar to gRPC.",
   "main": "./dist/cjs/index.js",
diff --git a/webview_rpc_runtime_library/src/core/webview_rpc_client.js b/webview_rpc_runtime_library/src/core/webview_rpc_client.js
index b4102c6..19d97bf 100644
--- a/webview_rpc_runtime_library/src/core/webview_rpc_client.js
+++ b/webview_rpc_runtime_library/src/core/webview_rpc_client.js
@@ -35,8 +35,7 @@ export class WebViewRpcClient {
             requestId,
             isRequest: true,
             method,
-            payload: requestPayload,
-            error: null
+            payload: requestPayload
         };
 
         // Create promise for this request
diff --git a/webview_rpc_runtime_library/src/core/webview_rpc_server.js b/webview_rpc_runtime_library/src/core/webview_rpc_server.js
index cb3c2cd..bf42a92 100644
--- a/webview_rpc_runtime_library/src/core/webview_rpc_server.js
+++ b/webview_rpc_runtime_library/src/core/webview_rpc_server.js
@@ -62,9 +62,8 @@ export class WebViewRpcServer {
         const responseEnvelope = {
             requestId: requestEnvelope.requestId,
             isRequest: false,
-            method: requestEnvelope.method,
-            payload: null,
-            error: null
+            method: requestEnvelope.method
+            // payload and error fields will be set only when needed
         };
 
         try {
diff --git a/webview_rpc_runtime_library/src/core/webview_rpc_utils.js b/webview_rpc_runtime_library/src/core/webview_rpc_utils.js
index b6bab5e..083148a 100644
--- a/webview_rpc_runtime_library/src/core/webview_rpc_utils.js
+++ b/webview_rpc_runtime_library/src/core/webview_rpc_utils.js
@@ -7,40 +7,61 @@ export function encodeEnvelopeToBase64(envObj) {
   
     const rawBytes = encodeRpcEnvelope(envObj);
     // rawBytes is Uint8Array
-    return base64FromBytes(rawBytes);
+    return uint8ArrayToBase64(rawBytes);
   }
 
   export function decodeEnvelopeFromBase64(base64Str) {
-    const bytes = base64ToBytes(base64Str);
+    const bytes = base64ToUint8Array(base64Str);
     // decodeRpcEnvelope(bytes) -> plain object { requestId, isRequest, ...}
     const messageObj = decodeRpcEnvelope(bytes);
     return messageObj;
   }
 
-/** Uint8Array -> Base64 (browser JS) */
-let isNode = typeof window === 'undefined';
+/**
+ * Base64 <-> Uint8Array conversion utilities
+ * (Browser and Node.js compatible)
+ */
 
-export function base64FromBytes(u8arr) {
-  if (isNode) {
-    return Buffer.from(u8arr).toString('base64');
-  } else {
-    let binary = "";
-    for (let i = 0; i < u8arr.length; i++) {
-      binary += String.fromCharCode(u8arr[i]); 
+/**
+ * Converts a Uint8Array to a Base64 string.
+ * @param {Uint8Array} bytes - The byte array to convert.
+ * @returns {string} The Base64 encoded string.
+ */
+export function uint8ArrayToBase64(bytes) {
+  if (typeof window !== 'undefined' && typeof window.btoa === 'function') {
+    // Browser environment
+    let binary = '';
+    for (let i = 0; i < bytes.length; i++) {
+      binary += String.fromCharCode(bytes[i]);
     }
-    return btoa(binary);
+    return window.btoa(binary);
+  } else if (typeof Buffer === 'function') {
+    // Node.js environment
+    return Buffer.from(bytes).toString('base64');
+  } else {
+    throw new Error('Unsupported environment for Base64 encoding');
   }
 }
 
-export function base64ToBytes(b64) {
-  if (isNode) {
-    return Buffer.from(b64, 'base64');
-  } else {
-    const bin = atob(b64);
-    const u8 = new Uint8Array(bin.length);
-    for (let i = 0; i < bin.length; i++) {
-      u8[i] = bin.charCodeAt(i);
+/**
+ * Converts a Base64 string to a Uint8Array.
+ * @param {string} base64 - The Base64 string to convert.
+ * @returns {Uint8Array} The decoded byte array.
+ */
+export function base64ToUint8Array(base64) {
+  if (typeof window !== 'undefined' && typeof window.atob === 'function') {
+    // Browser environment
+    const binary_string = window.atob(base64);
+    const len = binary_string.length;
+    const bytes = new Uint8Array(len);
+    for (let i = 0; i < len; i++) {
+      bytes[i] = binary_string.charCodeAt(i);
     }
-    return u8;
+    return bytes;
+  } else if (typeof Buffer === 'function') {
+    // Node.js environment
+    return new Uint8Array(Buffer.from(base64, 'base64'));
+  } else {
+    throw new Error('Unsupported environment for Base64 decoding');
   }
 }