key 값에 -(dash)가 들어 가면 RESP 포맷에 위배 되서 아래 에러를 발생
WRONGTYPE Operation against a key holding the wrong kind of value
참고 : http://redis.io/topics/protocol
RESP Errors
RESP has a specific data type for errors. Actually errors are exactly like RESP Simple Strings, but the first character is a minus '-' character instead of a plus. The real difference between Simple Strings and Errors in RESP is that errors are treated by clients as exceptions, and the string that composes the Error type is the error message itself.
The basic format is:
"-Error message\r\n"
Error replies are only sent when something wrong happens, for instance if you try to perform an operation against the wrong data type, or if the command does not exist and so forth. An exception should be raised by the library client when an Error Reply is received.
The following are examples of error replies:
-ERR unknown command 'foobar'
-WRONGTYPE Operation against a key holding the wrong kind of value
The first word after the "-", up to the first space or newline, represents the kind of error returned. This is just a convention used by Redis and is not part of the RESP Error format.
For example, ERR is the generic error, while WRONGTYPE is a more specific error that implies that the client tried to perform an operation against the wrong data type. This is called an Error Prefix and is a way to allow the client to understand the kind of error returned by the server without to rely on the exact message given, that may change over the time.
A client implementation may return different kind of exceptions for different errors, or may provide a generic way to trap errors by directly providing the error name to the caller as a string.
However, such a feature should not be considered vital as it is rarely useful, and a limited client implementation may simply return a generic error condition, such as false.
