Calling canisters without an argument requires a candid-bytes with no values?

Developers
1

Hello, when I call a canister method that doesn’t take any arguments without any bytes for the ‘arg’ it gives this error:
Call Reject: reject_code: 5: CANISTER_ERROR: Canister bayhi-7yaaa-aaaai-qahca-cai trapped explicitly: Custom(Cannot parse header
Caused by:
binary parser error: io error).

When I call a canister-method that doesn’t take any arguments with the ‘arg’ as these bytes: [68, 73, 68, 76, 0, 0] which is a candid-serialization of zero values, then it works.
Is this a documented feature/requirement or is this a bug? or is this something specific with the rust cdk function annotations?

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2

If your canister speaks Candid (as it it should unless you have very good reasons do do otherwise), then the argument needs to be encoded in Candid – even if it is just the empty argument sequence ().

Think of a REST API expecting JSON, even if you send no values, it might require you to send "{}" or maybe "[]".

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