Found more than one concrete type for given DbContext Type (xxx.xxxx.xxx) define MultiTenancySideAttribute with Tenant

错误提示：

Found more than one concrete type for given DbContext Type (Abp.Zero.EntityFramework.AbpZeroCommonDbContext`2[Easyman.Authorization.Roles.Role,Easyman.Users.User]) define MultiTenancySideAttribute with Tenant. Found types: Easyman.EntityFramework.EasymanDbContext, Easyman.EntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null, Easyman.EntityFramework.EmProjectDbContext, Em.Project.EntityFramework, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null.

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错误原由：找到满足User的映射的多个DbContext

我的项目中，EF有多级继承，继承结构如下：

public abstract class EasymanDbContext : AbpZeroDbContext<Tenant, Role, User>

public class EmProjectDbContext: EasymanDbContext

此处有一个细节处理：应该将继承AbpZeroDbContext的子类EasymanDbContext 设置为抽象类abstract，理由是抽象类不会被实例化