code: @ForbiddenWhenBuilding
      @Override
      public String getVar() {
          fwba.checkNotForbidden();
          if (cachedVar != null) {
              return cachedVar;
          } else {
              cachedVar = StringUtil.escape(columnConfig.getFieldName());
              return cachedVar;
          }
      }
docs: The variable/property name.
  @return the variable (aka property) name.