Convert the payload object to serialized form.
@param payload the Object to convert
@param headers optional headers for the message (may be {@code null})
@param conversionHint an extra object passed to the {@link MessageConverter},
e.g. the associated {@code MethodParameter} (may be {@code null}}
@return the resulting payload for the message, or {@code null} if the converter
cannot perform the conversion
@since 4.2
Convert the payload object to serialized form. @param payload the Object to convert @param headers optional headers for the message (may be {@code null}) @param conversionHint an extra object passed to the {@link MessageConverter}, e.g. the associated {@code MethodParameter} (may be {@code null}} @return the resulting payload for the message, or {@code null} if the converter cannot perform the conversion @since 4.2