String concatenation operator works wrong with null

s1+s2 throws NullPointerException if s1==null

=== Here is the minimized test demonstrating the bug ===
class jdk1_1_test {
   public static void main (String args[]) {
    String s=null;
    System.out.println("some string"+s);
    System.out.println(s+"yet another string");

  }
}
=== Test output under jdk1.1 ===
some stringnull
java.lang.NullPointerException
at java.lang.StringBuffer.<init>(StringBuffer.java)
at jdk1_1_test.main(jdk1_1_test.java:5)

=== Test output under jdk1.0.2 ===
some stringnull
nullyet another string

=== Here is the part of Java Language Specification 1.0 (Item 15.17.1) ===

Now only reference values need to be considered. If the
reference is null, it is converted to the string "null" (four
ASCII characters n, u, l, l). Otherwise, the conversion is
performed as if by an invocation of the toString method of the
referenced object with no arguments; but if the result of
invoking the toString method is null, then the string "null" is
used instead. The toString method (§20.1.2) is defined by the
primordial class Object (§20.1); many classes override it,
notably Boolean, Character, Integer, Long, Float, Double, and
String.