code: private void validateColumn(final Column<?> newColumn) {
          Preconditions.checkNotNull(newColumn, "Attempted to add a null to the columns in table " + name);
          List<String> stringList = new ArrayList<>();
          for (String name : columnNames()) {
              stringList.add(name.toLowerCase());
          }
          if (stringList.contains(newColumn.name().toLowerCase())) {
              String message = String.format("Cannot add column with duplicate name %s to table %s", newColumn, name);
              throw new IllegalArgumentException(message);
          }
  
          checkColumnSize(newColumn);
      }
docs: Throws an IllegalArgumentException if a column with the given name is already in the table, or if the number of
  rows in the column does not match the number of rows in the table