code: FluxConcatArray<T> concatAdditionalSourceLast(Publisher<? extends T> source) {
  		int n = array.length;
  		@SuppressWarnings("unchecked")
  		Publisher<? extends T>[] newArray = new Publisher[n + 1];
  		System.arraycopy(array, 0, newArray, 0, n);
  		newArray[n] = source;
  		
  		return new FluxConcatArray<>(delayError, newArray);
  	}
docs: Returns a new instance which has the additional source to be merged together with
  the current array of sources.
  <p>
  This operation doesn't change the current FluxMerge instance.
  
  @param source the new source to merge with the others
  @return the new FluxConcatArray instance