code: private void writeCollectionElement(Object o) throws IOException
      {
          if (o == null)
          {
              out.write("null");
          }
          else if (o instanceof Boolean || o instanceof Double)
          {
              writePrimitive(o, false);
          }
          else if (o instanceof Long)
          {
              writePrimitive(o, writeLongsAsStrings);
          }
          else if (o instanceof String)
          {   // Never do an @ref to a String (they are treated as logical primitives and intern'ed on read)
              writeJsonUtf8String((String) o, out);
          }
          else if (neverShowType && MetaUtils.isPrimitive(o.getClass()))
          {   // If neverShowType, then force primitives (and primitive wrappers)
              // to be output with toString() - prevents {"value":6} for example
              writePrimitive(o, false);
          }
          else
          {
              writeImpl(o, true);
          }
      }
docs: Write an element that is contained in some type of Collection or Map.
  @param o Collection element to output in JSON format.
  @throws IOException if an error occurs writing to the output stream.