Extract hospitalizations from this medical document. Return a JSON array or null.

Each entry:
- type: "admission", "emergency", "day_case"
- value: (empty)
- summary: reason + facility, e.g. "Shunt revision, Universitätsklinikum Ulm"
- timestamp: "YYYY-MM-DD" admission date if mentioned
- data: {"reason": "...", "facility": "...", "discharge": "YYYY-MM-DD", "duration_days": 5}

Every entry MUST come from text explicitly present in the document. Do NOT infer or assume.
Return null if nothing relevant is explicitly described.

Document:
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