泛型在Eclipse中可以编译和运行，但在javac中无法编译。

注意：这是从Comparable和Comparator与null相关的问题派生出来的。

这段代码在Eclipse（20090920-1017）中可以编译和运行正常。

import java.util.*;
public class SortNull {
   static >
   Comparator nullComparableComparator() {
      return new Comparator() {
         @Override public int compare(T el1, T el2) {
         return
            el1 == null ? -1 :
            el2 == null ? +1 :
            el1.compareTo(el2);
         }
      };
   }
   public static void main(String[] args) {
      List numbers = new ArrayList(
         Arrays.asList(3, 2, 1, null, null, 0)
      );
      Comparator numbersComp = nullComparableComparator();
      Collections.sort(numbers, numbersComp);
      System.out.println(numbers);
      // "[null, null, 0, 1, 2, 3]"
      List names = new ArrayList(
         Arrays.asList("Bob", null, "Alice", "Carol")
      );
      Comparator namesComp = nullComparableComparator();
      Collections.sort(names, namesComp);
      System.out.println(names);
      // "[null, Alice, Bob, Carol]"
   }
}

然而在javac 1.6.0_17上无法编译。以下是错误信息：

SortNull.java:17: incompatible types; no instance(s) of type variable(s) T exist
 so that java.util.Comparator conforms
 to java.util.Comparator
found   : java.util.Comparator
required: java.util.Comparator
     Comparator numbersComp = nullComparableComparator();
SortNull.java:25: incompatible types; no instance(s) of type variable(s) T exist
 so that java.util.Comparator conforms
 to java.util.Comparator
found   : java.util.Comparator
required: java.util.Comparator
     Comparator namesComp = nullComparableComparator();
2 errors

是否有人可以解释这个差异是为什么？这是一个错误吗？如果是的话，是谁有问题？