Retrieve OptionSet values without using the CRM SDK

{"Error in line 1 position 732. Element 'http://schemas.datacontract.org/2004/07/System.Collections.Generic:value'
contains data from a type that maps to the name 'http://schemas.microsoft.com/xrm/2011/Metadata:PicklistAttributeMetadata'.
The deserializer has no knowledge of any type that maps to this name. Consider using a DataContractResolver or add the type
corresponding to 'PicklistAttributeMetadata' to the list of known types - for example, by using the KnownTypeAttribute attribute
or by adding it to the list of known types passed to DataContractSerializer."}

OrganizationRequest request = new OrganizationRequest();
            request.RequestName = "RetrieveAttribute";
            request.Parameters = new ParameterCollection();

            request.Parameters.Add(new KeyValuePair<string, object>("EntityLogicalName", entityLogicalName));
            request.Parameters.Add(new KeyValuePair<string, object>("LogicalName", field));
            request.Parameters.Add(new KeyValuePair<string, object>("RetrieveAsIfPublished", true));
            request.Parameters.Add(new KeyValuePair<string, object>("MetadataId", Guid.Empty));

            OrganizationResponse response = (OrganizationResponse)service.Execute(request);