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5function msgSender()
6    internal
7    view
8    returns (address sender)
9{
10    if (msg.sender == address(this)) {
11        bytes memory array = msg.data;
12        uint256 index = msg.data.length;
13        assembly {
14            // Load the 32 bytes word from memory with the address on the lower 20 bytes, and mask those.
15            sender := and(
16                mload(add(array, index)),
17                0xffffffffffffffffffffffffffffffffffffffff
18            )
19        }
20    } else {
21        sender = msg.sender;
22    }
23    return sender;
24}