Creates a builder to create a new {@link AmqpMessage} copying the metadata from the passed message.
@param existing an existing message, must not be {@code null}. @return a builder to create an {@link AmqpMessage}.
See Implementation
Creates a builder to create a new {@link AmqpMessage} copying the metadata from the passed message.
@param existing an existing message, must not be {@code null}. @return a builder to create an {@link AmqpMessage}.