'Court' is considered an 'institution of human life and society' and a place, and as such, functions without the article-- 'at court', 'to court', 'in court'-- much like 'to hospital', 'at school', 'in church'. Hence, it is one member of a small group of exceptions to the rule for definite articles. 'The police', on the other hand is not an institution or place, but a group or department of law inforcement officers, and functions in this situation as a normal collective noun.
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