code: @Override
      public void visitTypeParameter(JCTypeParameter tree) {
          TypeVar a = (tree.type != null)
              ? (TypeVar)tree.type
              : new TypeVar(tree.name, env.info.scope.owner, syms.botType);
          tree.type = a;
          if (chk.checkUnique(tree.pos(), a.tsym, env.info.scope)) {
              env.info.scope.enter(a.tsym);
          }
          result = a;
      }
docs: Class enter visitor method for type parameters.
  Enter a symbol for type parameter in local scope, after checking that it
  is unique.