diff --git a/OnePasswordExtension.h b/OnePasswordExtension.h
index 6213dde..e91d9b7 100644
--- a/OnePasswordExtension.h
+++ b/OnePasswordExtension.h
@@ -13,6 +13,8 @@
 #import <WebKit/WebKit.h>
 #endif
 
+NS_ASSUME_NONNULL_BEGIN
+
 // Login Dictionary keys - Used to get or set the properties of a 1Password Login
 #define AppExtensionURLStringKey                  @"url_string"
 #define AppExtensionUsernameKey                   @"username"
@@ -85,7 +87,7 @@
 
  @param error Reply parameter that is nil if the 1Password Extension has been successfully completed, or it contains error information about the completion failure.
  */
-- (void)findLoginForURLString:(NSString *)URLString forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion;
+- (void)findLoginForURLString:(NSString *)URLString forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError *error))completion;
 
 /*!
  Create a new login within 1Password and allow the user to generate a new password before saving.
@@ -108,7 +110,7 @@
 
  @param error Reply parameter that is nil if the 1Password Extension has been successfully completed, or it contains error information about the completion failure.
  */
-- (void)storeLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDictionary passwordGenerationOptions:(NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion;
+- (void)storeLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDictionary passwordGenerationOptions:(nullable NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError * __nullable error))completion;
 
 /*!
  Change the password for an existing login within 1Password.
@@ -134,7 +136,7 @@
 
  @param error Reply parameter that is nil if the 1Password Extension has been successfully completed, or it contains error information about the completion failure.
  */
-- (void)changePasswordForLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDict passwordGenerationOptions:(NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion;
+- (void)changePasswordForLoginForURLString:(NSString *)URLString loginDetails:(nullable NSDictionary *)loginDetailsDict passwordGenerationOptions:(nullable NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError * __nullable error))completion;
 
 /*!
  Called from your web view controller, this method will show all the saved logins for the active page in the provided web
@@ -154,7 +156,7 @@
 
  @param error Reply parameter that is nil if the 1Password Extension has been successfully completed, or it contains error information about the completion failure.
  */
-- (void)fillItemIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(id)sender showOnlyLogins:(BOOL)yesOrNo completion:(void (^)(BOOL success, NSError *error))completion;
+- (void)fillItemIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(nullable id)sender showOnlyLogins:(BOOL)yesOrNo completion:(nullable void (^)(BOOL success, NSError * __nullable error))completion;
 
 /*!
  Called in the UIActivityViewController completion block to find out whether or not the user selected the 1Password Extension activity.
@@ -162,7 +164,7 @@
  @param the bundle identidier of the selected activity in the share sheet.
  @return YES if the selected activity is the 1Password extension, NO otherwise.
  */
-- (BOOL)isOnePasswordExtensionActivityType:(NSString *)activityType;
+- (BOOL)isOnePasswordExtensionActivityType:(nullable NSString *)activityType;
 
 /*!
  The returned NSExtensionItem can be used to create your own UIActivityViewController. Use `isOnePasswordExtensionActivityType:` and `fillReturnedItems:intoWebView:completion:` in the activity view controller completion block to process the result. The completion block is guaranteed to be called on the main thread.
@@ -173,7 +175,7 @@
 
  @param error Reply parameter that is nil if the 1Password extension item has been successfully created, or it contains error information about the completion failure.
  */
-- (void)createExtensionItemForWebView:(id)webView completion:(void (^)(NSExtensionItem *extensionItem, NSError *error))completion;
+- (void)createExtensionItemForWebView:(id)webView completion:(void (^)(NSExtensionItem * __nullable extensionItem, NSError * __nullable error))completion;
 
 /*!
  Method used in the UIActivityViewController completion block to fill information into a web view.
@@ -185,11 +187,13 @@
 
  @param error Reply parameter that is nil if the 1Password Extension has been successfully completed, or it contains error information about the completion failure.
  */
-- (void)fillReturnedItems:(NSArray *)returnedItems intoWebView:(id)webView completion:(void (^)(BOOL success, NSError *error))completion;
+- (void)fillReturnedItems:(NSArray *)returnedItems intoWebView:(id)webView completion:(nullable void (^)(BOOL success, NSError * __nullable error))completion;
 
 /*!
  Deprecated in version 1.3.
  @see Use fillItemIntoWebView:forViewController:sender:showOnlyLogins:completion: instead
  */
-- (void)fillLoginIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(BOOL success, NSError *error))completion __attribute__((deprecated("Use fillItemIntoWebView:forViewController:sender:showOnlyLogins:completion: instead. Deprecated in version 1.3")));
+- (void)fillLoginIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(BOOL success, NSError * __nullable error))completion __attribute__((deprecated("Use fillItemIntoWebView:forViewController:sender:showOnlyLogins:completion: instead. Deprecated in version 1.3")));
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/OnePasswordExtension.m b/OnePasswordExtension.m
index 28707b4..00e1fd2 100644
--- a/OnePasswordExtension.m
+++ b/OnePasswordExtension.m
@@ -55,7 +55,7 @@ - (BOOL)isAppExtensionAvailable {
 
 #pragma mark - Native app Login
 
-- (void)findLoginForURLString:(NSString *)URLString forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion {
+- (void)findLoginForURLString:(NSString *)URLString forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError * __nullable error))completion {
 	NSAssert(URLString != nil, @"URLString must not be nil");
 	NSAssert(viewController != nil, @"viewController must not be nil");
 
@@ -103,7 +103,7 @@ - (void)findLoginForURLString:(NSString *)URLString forViewController:(UIViewCon
 
 #pragma mark - New User Registration
 
-- (void)storeLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDictionary passwordGenerationOptions:(NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion {
+- (void)storeLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDictionary passwordGenerationOptions:(nullable NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError * __nullable error))completion {
 	NSAssert(URLString != nil, @"URLString must not be nil");
 	NSAssert(loginDetailsDictionary != nil, @"loginDetailsDict must not be nil");
 	NSAssert(viewController != nil, @"viewController must not be nil");
@@ -159,7 +159,7 @@ - (void)storeLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary
 
 #pragma mark - Change Password
 
-- (void)changePasswordForLoginForURLString:(NSString *)URLString loginDetails:(NSDictionary *)loginDetailsDict passwordGenerationOptions:(NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(NSDictionary *loginDictionary, NSError *error))completion {
+- (void)changePasswordForLoginForURLString:(NSString *)URLString loginDetails:(nullable NSDictionary *)loginDetailsDict passwordGenerationOptions:(nullable NSDictionary *)passwordGenerationOptions forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(NSDictionary * __nullable loginDictionary, NSError * __nullable error))completion {
 	NSAssert(URLString != nil, @"URLString must not be nil");
 	NSAssert(viewController != nil, @"viewController must not be nil");
 
@@ -214,7 +214,7 @@ - (void)changePasswordForLoginForURLString:(NSString *)URLString loginDetails:(N
 
 #pragma mark - Web View filling Support
 
-- (void)fillItemIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(id)sender showOnlyLogins:(BOOL)yesOrNo completion:(void (^)(BOOL success, NSError *error))completion {
+- (void)fillItemIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(nullable id)sender showOnlyLogins:(BOOL)yesOrNo completion:(nullable void (^)(BOOL success, NSError  * __nullable error))completion {
 	NSAssert(webView != nil, @"webView must not be nil");
 	NSAssert(viewController != nil, @"viewController must not be nil");
 
@@ -243,11 +243,11 @@ - (void)fillItemIntoWebView:(id)webView forViewController:(UIViewController *)vi
 
 #pragma mark - Support for custom UIActivityViewControllers
 
-- (BOOL)isOnePasswordExtensionActivityType:(NSString *)activityType {
+- (BOOL)isOnePasswordExtensionActivityType:(nullable NSString *)activityType {
 	return [@"com.agilebits.onepassword-ios.extension" isEqualToString:activityType] || [@"com.agilebits.beta.onepassword-ios.extension" isEqualToString:activityType];
 }
 
-- (void)createExtensionItemForWebView:(id)webView completion:(void (^)(NSExtensionItem *extensionItem, NSError *error))completion {
+- (void)createExtensionItemForWebView:(id)webView completion:(void (^)(NSExtensionItem * __nullable extensionItem, NSError * __nullable error))completion {
 	NSAssert(webView != nil, @"webView must not be nil");
 
 #ifdef __IPHONE_8_0
@@ -288,7 +288,9 @@ - (void)createExtensionItemForWebView:(id)webView completion:(void (^)(NSExtensi
 #endif
 }
 
-- (void)fillReturnedItems:(NSArray *)returnedItems intoWebView:(id)webView completion:(void (^)(BOOL success, NSError *error))completion {
+- (void)fillReturnedItems:(NSArray *)returnedItems intoWebView:(id)webView completion:(nullable void (^)(BOOL success, NSError * __nullable error))completion {
+	NSAssert(webView != nil, @"webView must not be nil");
+
 	if (returnedItems.count == 0) {
 		NSError *error = [OnePasswordExtension extensionCancelledByUserError];
 		if (completion) {
@@ -667,7 +669,7 @@ + (NSError *)failedToObtainURLStringFromWebViewError {
  Deprecated in version 1.3.
  Use fillItemIntoWebView:forViewController:sender:showOnlyLogins:completion: instead
  */
-- (void)fillLoginIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(id)sender completion:(void (^)(BOOL success, NSError *error))completion {
+- (void)fillLoginIntoWebView:(id)webView forViewController:(UIViewController *)viewController sender:(nullable id)sender completion:(nullable void (^)(BOOL success, NSError * __nullable error))completion {
 	[self fillItemIntoWebView:webView forViewController:viewController sender:sender showOnlyLogins:YES completion:completion];
 }