Add non-generic collection property to model:
public class ModelClass
{

public CustomerCollection Customers { get; set; }

}
public class CustomerCollection : Collection<Customer>
{
}

ConventionModelBuilder reports following error:

System.ArgumentException occurred
Message=Many to Many navigationProperties must return either List<T> or Collection<T>.
Parameter name: property
Source=System.Web.Http.OData
ParamName=property
StackTrace:

   at System.Web.Http.OData.Builder.NavigationPropertyConfiguration..ctor(PropertyInfo property, EdmMultiplicity multiplicity) in C:\dd\DevDiv\Offcycle\WPT\WebStackRuntime\runtime\src\System.Web.Http.OData\OData\Builder\NavigationPropertyConfiguration.cs:line 29

InnerException: