@API(status = API.Status.STABLE)
        @SuppressWarnings("unchecked")
        public @Nullable TypeToken<? extends C> senderType() {
            if (this.senderType == null) {
                return null;
            }
            return (TypeToken<? extends C>) TypeToken.get(this.senderType);
        }
Returns the required sender type for this builder.
<p>
Returns {@code null} when there is not a specific required sender type.

@return required sender type
cloud-core/src/main/java/org/incendo/cloud/Command.java