code: public StrBuilder append(final Object obj) {
          if (obj == null) {
              return appendNull();
          }
          if (obj instanceof CharSequence) {
              return append((CharSequence) obj);
          }
          return append(obj.toString());
      }
docs: Appends an object to this string builder.
  Appending null will call {@link #appendNull()}.
  
  @param obj  the object to append
  @return this, to enable chaining