Made the scope in API credentials non nullable

Author: pmathew92

auth0/src/main/java/com/auth0/android/authentication/AuthenticationAPIClient.kt

@@ -731,8 +731,8 @@ public class AuthenticationAPIClient @VisibleForTesting(otherwise = VisibleForTe
     }
 
     /**
-     * Requests new Credentials using a valid Refresh Token. You can request credentials for a specific API by passing its audience value. The default scopes configured for
-     * the API will be granted if you don't request any specific scopes.
+     * Requests new Credentials using a valid Refresh Token. You can request credentials for a specific API by passing its audience value. The default scopes
+     * configured for the API will be granted if you don't request any specific scopes.
      *
      *
      * This method will use the /oauth/token endpoint with the 'refresh_token' grant, and the response will include an id_token and an access_token if 'openid' scope was requested when the refresh_token was obtained.

auth0/src/main/java/com/auth0/android/result/APICredentials.kt

@@ -41,7 +41,7 @@ public data class APICredentials(
      * @return the granted scope.
      */
     @field:SerializedName("scope")
-    val scope: String?
+    val scope: String
 ) {
     override fun toString(): String {
         return "APICredentials( accessToken='xxxxx', type='$type', expiresAt='$expiresAt', scope='$scope')"
@@ -53,5 +53,6 @@ public data class APICredentials(
  * Converts a Credentials instance to an APICredentials instance.
  */
 internal fun Credentials.toAPICredentials(): APICredentials {
-    return APICredentials(accessToken, type, expiresAt, scope)
+    val newScope = scope ?: "openid"
+    return APICredentials(accessToken, type, expiresAt, newScope)
 }

auth0/src/test/java/com/auth0/android/authentication/storage/CredentialsManagerTest.kt

@@ -581,7 +581,7 @@ public class CredentialsManagerTest {
         val accessTokenExpiry = CredentialsMock.ONE_HOUR_AHEAD_MS
         val apiCredentials = ApiCredentialsMock.create(
             "token", "type",
-            Date(accessTokenExpiry), null
+            Date(accessTokenExpiry), "scope"
         )
         Mockito.`when`(storage.retrieveString("audience")).thenReturn(gson.toJson(apiCredentials))
         Mockito.`when`(storage.retrieveString("com.auth0.refresh_token")).thenReturn("refreshToken")

auth0/src/test/java/com/auth0/android/authentication/storage/SecureCredentialsManagerTest.kt

@@ -2306,7 +2306,7 @@ public class SecureCredentialsManagerTest {
             Date(CredentialsMock.CURRENT_TIME_MS + 10 * 1000),
             "scope"
         )
-        insertTestApiCredentials("audience", true, Date(accessTokenExpiry), null)
+        insertTestApiCredentials("audience", true, Date(accessTokenExpiry), "scope")
         Mockito.`when`(
             client.renewAuth("refreshToken", "audience", "newScope")
         ).thenReturn(request)
@@ -2351,7 +2351,7 @@ public class SecureCredentialsManagerTest {
             Date(CredentialsMock.CURRENT_TIME_MS + 10 * 1000),
             "scope"
         )
-        insertTestApiCredentials("audience", true, Date(accessTokenExpiry), null)
+        insertTestApiCredentials("audience", true, Date(accessTokenExpiry), "scope")
         Mockito.`when`(
             client.renewAuth("refreshToken", "audience", "newScope")
         ).thenReturn(request)
@@ -2439,7 +2439,7 @@ public class SecureCredentialsManagerTest {
         }
         val accessTokenExpiry = CredentialsMock.ONE_HOUR_AHEAD_MS
         insertTestApiCredentials(
-            "audience1", true, Date(accessTokenExpiry), null
+            "audience1", true, Date(accessTokenExpiry), "scope"
         )
         val retrievedCredentials = manager.awaitApiCredentials("audience1")
         MatcherAssert.assertThat(retrievedCredentials, Is.`is`(Matchers.notNullValue()))
@@ -3153,7 +3153,7 @@ public class SecureCredentialsManagerTest {
         audience: String,
         hasAccessToken: Boolean,
         willExpireAt: Date,
-        scope: String?
+        scope: String
     ): String {
         val storedCredentials = ApiCredentialsMock.create(
             if (hasAccessToken) "accessToken" else "",

auth0/src/test/java/com/auth0/android/result/ApiCredentialsMock.kt

@@ -10,7 +10,7 @@ public class ApiCredentialsMock {
             accessToken: String,
             type: String,
             expiresAt: Date,
-            scope: String?,
+            scope: String,
         ): APICredentials {
             return APICredentials(
                 accessToken, type, expiresAt, scope