diff --git a/auth0/src/main/java/com/auth0/android/authentication/AuthenticationAPIClient.java b/auth0/src/main/java/com/auth0/android/authentication/AuthenticationAPIClient.java
index 633b32f85..589e04ce6 100755
--- a/auth0/src/main/java/com/auth0/android/authentication/AuthenticationAPIClient.java
+++ b/auth0/src/main/java/com/auth0/android/authentication/AuthenticationAPIClient.java
@@ -26,6 +26,7 @@
 
 import android.content.Context;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.annotation.VisibleForTesting;
 
 import com.auth0.android.Auth0;
@@ -593,7 +594,7 @@ public ParameterizableRequest<UserProfile, AuthenticationException> tokenInfo(@N
      * @return a request to start
      */
     @NonNull
-    public DatabaseConnectionRequest<DatabaseUser, AuthenticationException> createUser(@NonNull String email, @NonNull String password, @NonNull String username, @NonNull String connection) {
+    public DatabaseConnectionRequest<DatabaseUser, AuthenticationException> createUser(@NonNull String email, @NonNull String password, @Nullable String username, @NonNull String connection) {
         HttpUrl url = HttpUrl.parse(auth0.getDomainUrl()).newBuilder()
                 .addPathSegment(DB_CONNECTIONS_PATH)
                 .addPathSegment(SIGN_UP_PATH)
@@ -635,7 +636,6 @@ public DatabaseConnectionRequest<DatabaseUser, AuthenticationException> createUs
      */
     @NonNull
     public DatabaseConnectionRequest<DatabaseUser, AuthenticationException> createUser(@NonNull String email, @NonNull String password, @NonNull String connection) {
-        //noinspection ConstantConditions
         return createUser(email, password, null, connection);
     }
 
diff --git a/auth0/src/main/java/com/auth0/android/authentication/request/DelegationRequest.java b/auth0/src/main/java/com/auth0/android/authentication/request/DelegationRequest.java
index 3cd093614..5c08755f9 100755
--- a/auth0/src/main/java/com/auth0/android/authentication/request/DelegationRequest.java
+++ b/auth0/src/main/java/com/auth0/android/authentication/request/DelegationRequest.java
@@ -25,7 +25,6 @@
 package com.auth0.android.authentication.request;
 
 import android.support.annotation.NonNull;
-import android.support.annotation.Nullable;
 
 import com.auth0.android.Auth0Exception;
 import com.auth0.android.authentication.AuthenticationException;
diff --git a/auth0/src/main/java/com/auth0/android/authentication/request/ProfileRequest.java b/auth0/src/main/java/com/auth0/android/authentication/request/ProfileRequest.java
index e2305e119..77982d253 100755
--- a/auth0/src/main/java/com/auth0/android/authentication/request/ProfileRequest.java
+++ b/auth0/src/main/java/com/auth0/android/authentication/request/ProfileRequest.java
@@ -141,11 +141,13 @@ public void start(@NonNull final BaseCallback<Authentication, AuthenticationExce
         getAuthRequest().start(new BaseCallback<Credentials, AuthenticationException>() {
             @Override
             public void onSuccess(@Nullable final Credentials credentials) {
+                //noinspection ConstantConditions
                 userInfoRequest
                         .addHeader(HEADER_AUTHORIZATION, "Bearer " + credentials.getAccessToken())
                         .start(new BaseCallback<UserProfile, AuthenticationException>() {
                             @Override
                             public void onSuccess(@Nullable UserProfile profile) {
+                                //noinspection ConstantConditions
                                 callback.onSuccess(new Authentication(profile, credentials));
                             }
 
diff --git a/auth0/src/main/java/com/auth0/android/authentication/storage/SecureCredentialsManager.java b/auth0/src/main/java/com/auth0/android/authentication/storage/SecureCredentialsManager.java
index 4a9e0d046..7df456540 100644
--- a/auth0/src/main/java/com/auth0/android/authentication/storage/SecureCredentialsManager.java
+++ b/auth0/src/main/java/com/auth0/android/authentication/storage/SecureCredentialsManager.java
@@ -275,6 +275,7 @@ private void continueGetCredentials(final BaseCallback<Credentials, CredentialsM
             @Override
             public void onSuccess(@Nullable Credentials fresh) {
                 //non-empty refresh token for refresh token rotation scenarios
+                //noinspection ConstantConditions
                 String updatedRefreshToken = isEmpty(fresh.getRefreshToken()) ? credentials.getRefreshToken() : fresh.getRefreshToken();
                 Credentials refreshed = new Credentials(fresh.getIdToken(), fresh.getAccessToken(), fresh.getType(), updatedRefreshToken, fresh.getExpiresAt(), fresh.getScope());
                 saveCredentials(refreshed);
diff --git a/auth0/src/main/java/com/auth0/android/callback/BaseCallback.java b/auth0/src/main/java/com/auth0/android/callback/BaseCallback.java
index eb018a431..013cec17f 100755
--- a/auth0/src/main/java/com/auth0/android/callback/BaseCallback.java
+++ b/auth0/src/main/java/com/auth0/android/callback/BaseCallback.java
@@ -24,7 +24,7 @@
 
 package com.auth0.android.callback;
 
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.auth0.android.Auth0Exception;
 
@@ -38,6 +38,6 @@ public interface BaseCallback<T, U extends Auth0Exception> extends Callback<U> {
      *
      * @param payload Request payload or null
      */
-    void onSuccess(@NonNull T payload);
+    void onSuccess(@Nullable T payload);
 
 }
diff --git a/auth0/src/main/java/com/auth0/android/provider/OAuthManager.java b/auth0/src/main/java/com/auth0/android/provider/OAuthManager.java
index df893820a..35ec5e46d 100644
--- a/auth0/src/main/java/com/auth0/android/provider/OAuthManager.java
+++ b/auth0/src/main/java/com/auth0/android/provider/OAuthManager.java
@@ -231,6 +231,7 @@ public void onFailure(@NonNull TokenValidationException error) {
 
             @Override
             public void onSuccess(@Nullable SignatureVerifier signatureVerifier) {
+                //noinspection ConstantConditions
                 IdTokenVerificationOptions options = new IdTokenVerificationOptions(idTokenVerificationIssuer, apiClient.getClientId(), signatureVerifier);
                 String maxAge = parameters.get(KEY_MAX_AGE);
                 if (!TextUtils.isEmpty(maxAge)) {
diff --git a/auth0/src/main/java/com/auth0/android/provider/PKCE.java b/auth0/src/main/java/com/auth0/android/provider/PKCE.java
index ac855e0fd..1aa2f04b1 100644
--- a/auth0/src/main/java/com/auth0/android/provider/PKCE.java
+++ b/auth0/src/main/java/com/auth0/android/provider/PKCE.java
@@ -88,6 +88,7 @@ public void getToken(String authorizationCode, @NonNull final AuthCallback callb
                 .start(new BaseCallback<Credentials, AuthenticationException>() {
                     @Override
                     public void onSuccess(@Nullable Credentials payload) {
+                        //noinspection ConstantConditions
                         callback.onSuccess(payload);
                     }
 
diff --git a/auth0/src/main/java/com/auth0/android/provider/SignatureVerifier.java b/auth0/src/main/java/com/auth0/android/provider/SignatureVerifier.java
index 6d7eb356a..f457da555 100644
--- a/auth0/src/main/java/com/auth0/android/provider/SignatureVerifier.java
+++ b/auth0/src/main/java/com/auth0/android/provider/SignatureVerifier.java
@@ -59,6 +59,7 @@ static void forAsymmetricAlgorithm(@Nullable final String keyId, @NonNull Authen
         apiClient.fetchJsonWebKeys().start(new AuthenticationCallback<Map<String, PublicKey>>() {
             @Override
             public void onSuccess(@Nullable Map<String, PublicKey> jwks) {
+                //noinspection ConstantConditions
                 PublicKey publicKey = jwks.get(keyId);
                 try {
                     callback.onSuccess(new AsymmetricSignatureVerifier(publicKey));
diff --git a/auth0/src/main/java/com/auth0/android/provider/VoidCallback.java b/auth0/src/main/java/com/auth0/android/provider/VoidCallback.java
index a2c1aec09..575cdf59b 100644
--- a/auth0/src/main/java/com/auth0/android/provider/VoidCallback.java
+++ b/auth0/src/main/java/com/auth0/android/provider/VoidCallback.java
@@ -24,8 +24,6 @@
 
 package com.auth0.android.provider;
 
-import android.support.annotation.Nullable;
-
 import com.auth0.android.Auth0Exception;
 import com.auth0.android.callback.BaseCallback;
 
@@ -34,6 +32,4 @@
  */
 @SuppressWarnings("WeakerAccess")
 public interface VoidCallback extends BaseCallback<Void, Auth0Exception> {
-    @Override
-    void onSuccess(@Nullable Void payload);
 }
\ No newline at end of file
diff --git a/auth0/src/main/java/com/auth0/android/provider/WebAuthProvider.java b/auth0/src/main/java/com/auth0/android/provider/WebAuthProvider.java
index 4cbbc014a..0eec97bd8 100644
--- a/auth0/src/main/java/com/auth0/android/provider/WebAuthProvider.java
+++ b/auth0/src/main/java/com/auth0/android/provider/WebAuthProvider.java
@@ -139,6 +139,7 @@ public void start(@NonNull Context context, @NonNull VoidCallback callback) {
             if (returnToUrl == null) {
                 returnToUrl = CallbackHelper.getCallbackUri(scheme, context.getApplicationContext().getPackageName(), account.getDomainUrl());
             }
+            //noinspection ConstantConditions
             LogoutManager logoutManager = new LogoutManager(this.account, callback, returnToUrl);
             logoutManager.setCustomTabsOptions(ctOptions);
 
diff --git a/auth0/src/main/java/com/auth0/android/request/internal/ManagementErrorBuilder.java b/auth0/src/main/java/com/auth0/android/request/internal/ManagementErrorBuilder.java
index ae9561939..339c93931 100644
--- a/auth0/src/main/java/com/auth0/android/request/internal/ManagementErrorBuilder.java
+++ b/auth0/src/main/java/com/auth0/android/request/internal/ManagementErrorBuilder.java
@@ -1,6 +1,7 @@
 package com.auth0.android.request.internal;
 
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.auth0.android.Auth0Exception;
 import com.auth0.android.management.ManagementException;
@@ -30,7 +31,7 @@ public ManagementException from(@NonNull Map<String, Object> values) {
 
     @NonNull
     @Override
-    public ManagementException from(@NonNull String payload, int statusCode) {
+    public ManagementException from(@Nullable String payload, int statusCode) {
         return new ManagementException(payload, statusCode);
     }
 }
diff --git a/auth0/src/test/java/com/auth0/android/authentication/AuthenticationAPIClientTest.java b/auth0/src/test/java/com/auth0/android/authentication/AuthenticationAPIClientTest.java
index f7d03b8dc..997d79fef 100755
--- a/auth0/src/test/java/com/auth0/android/authentication/AuthenticationAPIClientTest.java
+++ b/auth0/src/test/java/com/auth0/android/authentication/AuthenticationAPIClientTest.java
@@ -843,7 +843,6 @@ public void shouldNotSendNullUsernameOnSignUp() throws Exception {
         mockAPI.willReturnSuccessfulSignUp();
 
         final MockAuthenticationCallback<DatabaseUser> callback = new MockAuthenticationCallback<>();
-        //noinspection ConstantConditions
         client.createUser(SUPPORT_AUTH0_COM, PASSWORD, null, MY_CONNECTION)
                 .start(callback);
 
@@ -864,7 +863,6 @@ public void shouldNotSendNullUsernameOnSignUp() throws Exception {
     public void shouldNotSendNullUsernameOnSignUpSync() throws Exception {
         mockAPI.willReturnSuccessfulSignUp();
 
-        //noinspection ConstantConditions
         final DatabaseUser user = client.createUser(SUPPORT_AUTH0_COM, PASSWORD, null, MY_CONNECTION)
                 .execute();
 
diff --git a/auth0/src/test/java/com/auth0/android/authentication/storage/CredentialsManagerTest.java b/auth0/src/test/java/com/auth0/android/authentication/storage/CredentialsManagerTest.java
index fc205bd96..1faf82cc3 100644
--- a/auth0/src/test/java/com/auth0/android/authentication/storage/CredentialsManagerTest.java
+++ b/auth0/src/test/java/com/auth0/android/authentication/storage/CredentialsManagerTest.java
@@ -172,13 +172,13 @@ public void shouldThrowOnSetIfCredentialsDoesNotHaveIdTokenOrAccessToken() {
         manager.saveCredentials(credentials);
     }
 
-    @SuppressWarnings("ConstantConditions")
     @Test
     public void shouldThrowOnSetIfCredentialsDoesNotHaveExpiresAt() {
         exception.expect(CredentialsManagerException.class);
         exception.expectMessage("Credentials must have a valid date of expiration and a valid access_token or id_token value.");
 
         Date date = null;
+        //noinspection ConstantConditions
         Credentials credentials = new CredentialsMock("idToken", "accessToken", "type", "refreshToken", date, "scope");
         manager.saveCredentials(credentials);
     }
diff --git a/auth0/src/test/java/com/auth0/android/authentication/storage/SecureCredentialsManagerTest.java b/auth0/src/test/java/com/auth0/android/authentication/storage/SecureCredentialsManagerTest.java
index 389b71e9f..69b82a3d5 100644
--- a/auth0/src/test/java/com/auth0/android/authentication/storage/SecureCredentialsManagerTest.java
+++ b/auth0/src/test/java/com/auth0/android/authentication/storage/SecureCredentialsManagerTest.java
@@ -277,13 +277,13 @@ public void shouldThrowOnSaveIfCredentialsDoesNotHaveIdTokenOrAccessToken() {
         manager.saveCredentials(credentials);
     }
 
-    @SuppressWarnings("ConstantConditions")
     @Test
     public void shouldThrowOnSaveIfCredentialsDoesNotHaveExpiresAt() {
         exception.expect(CredentialsManagerException.class);
         exception.expectMessage("Credentials must have a valid date of expiration and a valid access_token or id_token value.");
 
         Date date = null;
+        //noinspection ConstantConditions
         Credentials credentials = new CredentialsMock("idToken", "accessToken", "type", "refreshToken", date, "scope");
         prepareJwtDecoderMock(new Date());
         manager.saveCredentials(credentials);
diff --git a/auth0/src/test/java/com/auth0/android/authentication/storage/SharedPreferencesStorageTest.java b/auth0/src/test/java/com/auth0/android/authentication/storage/SharedPreferencesStorageTest.java
index 9043137ff..0d7d7a183 100644
--- a/auth0/src/test/java/com/auth0/android/authentication/storage/SharedPreferencesStorageTest.java
+++ b/auth0/src/test/java/com/auth0/android/authentication/storage/SharedPreferencesStorageTest.java
@@ -67,11 +67,11 @@ public void shouldCreateWithCustomPreferencesFileName() {
         verify(context).getSharedPreferences("my-preferences-file", Context.MODE_PRIVATE);
     }
 
-    @SuppressWarnings("ConstantConditions")
     @Test
     public void shouldThrowOnCreateIfCustomPreferencesFileNameIsNull() {
         exception.expect(IllegalArgumentException.class);
         exception.expectMessage("The SharedPreferences name is invalid");
+        //noinspection ConstantConditions
         new SharedPreferencesStorage(context, null);
     }
 
@@ -184,11 +184,11 @@ public void shouldRetrieveBooleanValueFromPreferences() {
 
     //Remove
 
-    @SuppressWarnings("ConstantConditions")
     @Test
     public void shouldRemovePreferencesKeyOnNullStringValue() {
         SharedPreferencesStorage storage = new SharedPreferencesStorage(context);
         String value = null;
+        //noinspection ConstantConditions
         storage.store("name", value);
         verify(sharedPreferencesEditor).remove("name");
         verify(sharedPreferencesEditor).apply();