code: def v_unique_name_leaf_list(ctx, stmt):
      
  
      if not stmt.i_config:
          return
      seen = []
      for defval in stmt.i_default:
          if defval in seen:
              err_add(ctx.errors, stmt.pos, 'DUPLICATE_DEFAULT', (defval))
          else:
              seen.append(defval)
docs: Make sure config true leaf-lists do nothave duplicate defaults