Update src/main/java/com/auth0/client/mgmt/ManagementAPI.java

Author: krrrr38

src/main/java/com/auth0/client/mgmt/ManagementAPI.java

@@ -409,7 +409,7 @@ public NetworkAclsEntity networkAcls() {
      */
     public static class Builder {
         private final String domain;
-        private TokenProvider tokenProvider;
+        private final TokenProvider tokenProvider;
         private Auth0HttpClient httpClient = DefaultHttpClient.newBuilder().build();
 
         /**