fix: logic bug in template contract MessageEmitter.sol

[anirudhwarrier]

Identified in https://github.com/smartcontractkit/cre-workflows/pull/472#discussion_r2754016483

Logic Bug in getMessage

Location:

Solidity

function getMessage(address emitter, uint256 timestamp) public view returns (string memory) {
    bytes32 key = _hashKey(emitter, timestamp);
    require(bytes(s_messages[key]).length == 0, "Message does not exist for the given sender and timestamp");
    return s_messages[key];
}

Problem:

The require checks that the message length is zero (== 0), and reverts with "Message does not exist for the given sender and timestamp".
But a message does exist only if the length is greater than 0. This logic is inverted: it's allowing "empty" messages and reverting if present.

Fix:

The condition should be > 0, not == 0:

Solidity

require(bytes(s_messages[key]).length > 0, "Message does not exist for the given sender and timestamp");