code: public <T> Source<T> from(Supplier<T> supplier) {
  		Assert.notNull(supplier, "Supplier must not be null");
  		Source<T> source = getSource(supplier);
  		if (this.sourceOperator != null) {
  			source = this.sourceOperator.apply(source);
  		}
  		return source;
  	}
docs: Return a new {@link Source} from the specified value supplier that can be used to
  perform the mapping.
  @param <T> the source type
  @param supplier the value supplier
  @return a {@link Source} that can be used to complete the mapping
  @see #from(Object)