collection_exists returns 404 due to wrong route instead of validating invalid names

[woaiqjj]

Description

When calling collection_exists with invalid collection names (such as empty string or control characters), the client constructs an incorrect request path like:

/collections//exists

This leads the server to return:

404 Not Found
{"status":{"error":"Not found: Collection `exists` doesn't exist!"}}

This is not a genuine “not found” error, but a parameter validation issue. The request should have been rejected before reaching the REST route.

---

🔬 Reproduction Code

from qdrant_client import QdrantClient

client = QdrantClient(url="http://localhost:6333")

for name in ["", "\t", "\n"]:
    try:
        client.collection_exists(collection_name=name)
    except Exception as e:
        print(f"{repr(name)} -> {type(e).__name__}: {e}")

---

🧩 Current Behavior

• The SDK/server generates /collections//exists for invalid names.
• The server responds with 404 and message: "Collection \exists doesn't exist!"

---

✅ Expected Behavior

• Invalid collection names (empty or control characters) should not reach the route handler.
• SDK or server should validate input and return a clear error response:
  • HTTP 400 Bad Request, or
  • HTTP 422 Unprocessable Entity
• The error message should explicitly state that the collection_name is invalid, rather than implying a missing "exists" collection.

---

💡 Suggested Fix

• Option A (SDK level): Validate collection_name before sending the request and raise a ValueError if invalid.
• Option B (Server level): Validate path parameters and return 400/422 with an appropriate error message ("Invalid collection name").

---

🧪 Environment

Component	Version / Value
Qdrant	v1.15.5
Python SDK	qdrant-client==1.14.2
Endpoint	http://localhost:6333

[chen0427ok]

I’ve opened a PR #7709 to fix this