code: public StrBuilder appendWithSeparators(final Iterable<?> iterable, final String separator) {
          if (iterable != null) {
              final String sep = Objects.toString(separator, "");
              final Iterator<?> it = iterable.iterator();
              while (it.hasNext()) {
                  append(it.next());
                  if (it.hasNext()) {
                      append(sep);
                  }
              }
          }
          return this;
      }
docs: Appends an iterable placing separators between each value, but
  not before the first or after the last.
  Appending a null iterable will have no effect.
  Each object is appended using {@link #append(Object)}.
  
  @param iterable  the iterable to append
  @param separator  the separator to use, null means no separator
  @return this, to enable chaining