只有当注入器内部提供商注册表中存在与令牌对应的提供商时，注入器才能为这个令牌创建一个依赖值。
An injector can only create a value for a given token if it has a provider for that token in its internal provider registry.
只有当注入器内部提供商注册表中存在与令牌对应的提供商时，注入器才能为这个令牌创建一个依赖值。
An injector can only create a value for a given token if it has a provider for that token in its internal provider registry.
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