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MessaggeStore.sol

pragma solidity ^0.5.0;

contract MessageStore {
    string private _message;
    address private _owner;
    
    constructor() public{
        _owner = msg.sender;
    }
    
    function getMessage() public view returns (string memory){
        return _message;
    }
    
    function setMessage(string memory newMessage) public onlyOwner{
        _message = newMessage;
    }
    
    modifier onlyOwner {
        require(msg.sender == _owner);
        _;
    }
}