code: @Nonnull
    public static String getConcatenatedOnDemand (@Nullable final String sFront,
                                                  @Nullable final String sSep,
                                                  @Nullable final String sEnd)
    {
      final StringBuilder aSB = new StringBuilder ();
      if (hasText (sFront))
      {
        aSB.append (sFront);
        if (hasText (sSep) && hasText (sEnd))
          aSB.append (sSep);
      }
      if (hasText (sEnd))
        aSB.append (sEnd);
      return aSB.toString ();
    }
docs: Concatenate the strings sFront and sEnd by the "sSep" string. If either front
  or back is <code>null</code> or empty, the separator is not applied.
  
  @param sFront
  Front string. May be <code>null</code>.
  @param sSep
  Separator string. May be <code>null</code>.
  @param sEnd
  May be <code>null</code>.
  @return The concatenated string.