diff --git a/src/appConfigurationImpl.ts b/src/appConfigurationImpl.ts
index a2ab128..42cebc5 100644
--- a/src/appConfigurationImpl.ts
+++ b/src/appConfigurationImpl.ts
@@ -98,18 +98,18 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     #sentinels: Map<WatchedSetting, SettingWatcher> = new Map();
     #watchAll: boolean = false;
     #kvRefreshInterval: number = DEFAULT_REFRESH_INTERVAL_IN_MS;
-    #kvRefreshTimer: RefreshTimer;
+    #kvRefreshTimer: RefreshTimer | undefined = undefined;
 
     // Feature flags
     #featureFlagEnabled: boolean = false;
     #featureFlagRefreshEnabled: boolean = false;
     #ffRefreshInterval: number = DEFAULT_REFRESH_INTERVAL_IN_MS;
-    #ffRefreshTimer: RefreshTimer;
+    #ffRefreshTimer: RefreshTimer | undefined = undefined;
 
     // Key Vault references
     #secretRefreshEnabled: boolean = false;
     #secretReferences: ConfigurationSetting[] = []; // cached key vault references
-    #secretRefreshTimer: RefreshTimer;
+    #secretRefreshTimer: RefreshTimer | undefined = undefined;
     #resolveSecretsInParallel: boolean = false;
 
     /**
@@ -126,7 +126,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
 
     constructor(
         clientManager: ConfigurationClientManager,
-        options: AzureAppConfigurationOptions | undefined,
+        options?: AzureAppConfigurationOptions,
     ) {
         this.#options = options;
         this.#clientManager = clientManager;
@@ -415,7 +415,8 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
                         postAttempts += 1;
                         backoffDuration = getExponentialBackoffDuration(postAttempts);
                     }
-                    console.warn(`Failed to load. Error message: ${error.message}. Retrying in ${backoffDuration} ms.`);
+                    const errorMessage = error instanceof Error ? error.message : String(error);
+                    console.warn(`Failed to load. Error message: ${errorMessage}. Retrying in ${backoffDuration} ms.`);
                     await new Promise(resolve => setTimeout(resolve, backoffDuration));
                 }
             } while (!abortSignal.aborted);
@@ -690,7 +691,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
      */
     async #refreshFeatureFlags(): Promise<boolean> {
         // if still within refresh interval/backoff, return
-        if (this.#ffRefreshInterval === undefined || !this.#ffRefreshTimer.canRefresh()) {
+        if (this.#ffRefreshInterval === undefined || !this.#ffRefreshTimer!.canRefresh()) {
             return Promise.resolve(false);
         }
 
@@ -699,7 +700,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
             await this.#loadFeatureFlags();
         }
 
-        this.#ffRefreshTimer.reset();
+        this.#ffRefreshTimer!.reset();
         return Promise.resolve(needRefresh);
     }
 
@@ -728,7 +729,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
      * @returns true if key-value collection has changed, false otherwise.
      */
     async #checkConfigurationSettingsChange(selectors: PagedSettingsWatcher[]): Promise<boolean> {
-        const funcToExecute = async (client) => {
+        const funcToExecute = async (client: AppConfigurationClient) => {
             for (const selector of selectors) {
                 if (selector.snapshotName) { // skip snapshot selector
                     continue;
@@ -765,7 +766,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
      * Gets a configuration setting by key and label.If the setting is not found, return undefine instead of throwing an error.
      */
     async #getConfigurationSetting(configurationSettingId: ConfigurationSettingId, getOptions?: GetConfigurationSettingOptions): Promise<GetConfigurationSettingResponse | undefined> {
-        const funcToExecute = async (client) => {
+        const funcToExecute = async (client: AppConfigurationClient) => {
             return getConfigurationSettingWithTrace(
                 this.#requestTraceOptions,
                 client,
@@ -788,7 +789,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     }
 
     async #listConfigurationSettings(listOptions: ListConfigurationSettingsOptions): Promise<{ items: ConfigurationSetting[]; pageWatchers: SettingWatcher[] }> {
-        const funcToExecute = async (client) => {
+        const funcToExecute = async (client: AppConfigurationClient) => {
             const pageWatchers: SettingWatcher[] = [];
             const pageIterator = listConfigurationSettingsWithTrace(
                 this.#requestTraceOptions,
@@ -808,7 +809,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     }
 
     async #getSnapshot(snapshotName: string, getOptions?: GetSnapshotOptions): Promise<GetSnapshotResponse | undefined> {
-        const funcToExecute = async (client) => {
+        const funcToExecute = async (client: AppConfigurationClient) => {
             return getSnapshotWithTrace(
                 this.#requestTraceOptions,
                 client,
@@ -831,7 +832,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
     }
 
     async #listConfigurationSettingsForSnapshot(snapshotName: string, listOptions?: ListConfigurationSettingsForSnapshotOptions): Promise<ConfigurationSetting[]> {
-        const funcToExecute = async (client) => {
+        const funcToExecute = async (client: AppConfigurationClient) => {
             const pageIterator = listConfigurationSettingsForSnapshotWithTrace(
                 this.#requestTraceOptions,
                 client,
diff --git a/src/common/contentType.ts b/src/common/contentType.ts
index 4891f42..829cc45 100644
--- a/src/common/contentType.ts
+++ b/src/common/contentType.ts
@@ -8,7 +8,7 @@ export type ContentType = {
     parameters: Record<string, string>;
 }
 
-export function parseContentType(contentTypeValue: string | undefined): ContentType | undefined {
+export function parseContentType(contentTypeValue?: string): ContentType | undefined {
     if (!contentTypeValue) {
         return undefined;
     }
@@ -27,7 +27,7 @@ export function parseContentType(contentTypeValue: string | undefined): ContentT
 
 // Determine whether a content type string is a valid JSON content type.
 // https://docs.microsoft.com/en-us/azure/azure-app-configuration/howto-leverage-json-content-type
-export function isJsonContentType(contentType: ContentType | undefined): boolean {
+export function isJsonContentType(contentType?: ContentType): boolean {
     const mediaType = contentType?.mediaType;
     if (!mediaType) {
         return false;
@@ -45,7 +45,7 @@ export function isJsonContentType(contentType: ContentType | undefined): boolean
     return typeParts[1].split("+").includes("json");
 }
 
-export function isFeatureFlagContentType(contentType: ContentType | undefined): boolean {
+export function isFeatureFlagContentType(contentType?: ContentType): boolean {
     const mediaType = contentType?.mediaType;
     if (!mediaType) {
         return false;
@@ -53,7 +53,7 @@ export function isFeatureFlagContentType(contentType: ContentType | undefined):
     return mediaType === featureFlagContentType;
 }
 
-export function isSecretReferenceContentType(contentType: ContentType | undefined): boolean {
+export function isSecretReferenceContentType(contentType?: ContentType): boolean {
     const mediaType = contentType?.mediaType;
     if (!mediaType) {
         return false;
diff --git a/src/keyvault/keyVaultKeyValueAdapter.ts b/src/keyvault/keyVaultKeyValueAdapter.ts
index e16fbd2..2e8eb4d 100644
--- a/src/keyvault/keyVaultKeyValueAdapter.ts
+++ b/src/keyvault/keyVaultKeyValueAdapter.ts
@@ -16,7 +16,7 @@ export class AzureKeyVaultKeyValueAdapter implements IKeyValueAdapter {
     #keyVaultOptions: KeyVaultOptions | undefined;
     #keyVaultSecretProvider: AzureKeyVaultSecretProvider;
 
-    constructor(keyVaultOptions: KeyVaultOptions | undefined, refreshTimer?: RefreshTimer) {
+    constructor(keyVaultOptions?: KeyVaultOptions, refreshTimer?: RefreshTimer) {
         this.#keyVaultOptions = keyVaultOptions;
         this.#keyVaultSecretProvider = new AzureKeyVaultSecretProvider(keyVaultOptions, refreshTimer);
     }
diff --git a/src/keyvault/keyVaultSecretProvider.ts b/src/keyvault/keyVaultSecretProvider.ts
index 2d5e113..fa3d825 100644
--- a/src/keyvault/keyVaultSecretProvider.ts
+++ b/src/keyvault/keyVaultSecretProvider.ts
@@ -14,7 +14,7 @@ export class AzureKeyVaultSecretProvider {
     #secretClients: Map<string, SecretClient>; // map key vault hostname to corresponding secret client
     #cachedSecretValues: Map<string, any> = new Map<string, any>(); // map secret identifier to secret value
 
-    constructor(keyVaultOptions: KeyVaultOptions | undefined, refreshTimer?: RefreshTimer) {
+    constructor(keyVaultOptions?: KeyVaultOptions, refreshTimer?: RefreshTimer) {
         if (keyVaultOptions?.secretRefreshIntervalInMs !== undefined) {
             if (refreshTimer === undefined) {
                 throw new ArgumentError("Refresh timer must be specified when Key Vault secret refresh is enabled.");