I know that it's correct to say 日本語教室, and it's also correct to say 日本語の教室. I am confused by 日本語教室. From my understanding, the particle の connects 2 nouns. For example, さくら大学の学生 (there is no particle before
university because さくら大学 is one name).
Please explain why 日本語教室 is OK. When can I omit の？ And when is it impossible to do?
Thank you very much!