Update `MockCookie#parse(String)` validation

[ngocnhan-tran1996]

spring-framework/spring-test/src/main/java/org/springframework/mock/web/MockCookie.java

Lines 130 to 132 in 68e6acd

	* Factory method that parses the value of the supplied "Set-Cookie" header.
	* @param setCookieHeader the "Set-Cookie" value; never {@code null} or empty
	* @return the created cookie

Based on the Javadoc, I think it should throw Set-Cookie header must not be null or empty instead of Invalid Set-Cookie header '' when setCookieHeader is empty.

See 8b89493 and 27a85be for the related changes.