Return the original {@code MessageHeaderAccessor} used to create the headers
of the given {@code Message}, or {@code null} if that's not available or if
its type does not match the required type.
<p>This is for cases where the existence of an accessor is strongly expected
(followed up with an assertion) or where an accessor will be created otherwise.
@param message the message to get an accessor for
@param requiredType the required accessor type (or {@code null} for any)
@return an accessor instance of the specified type, or {@code null} if none
@since 4.1
Return the original {@code MessageHeaderAccessor} used to create the headers of the given {@code Message}, or {@code null} if that's not available or if its type does not match the required type. <p>This is for cases where the existence of an accessor is strongly expected (followed up with an assertion) or where an accessor will be created otherwise. @param message the message to get an accessor for @param requiredType the required accessor type (or {@code null} for any) @return an accessor instance of the specified type, or {@code null} if none @since 4.1