The problem seems to be use of a varargs constructor while defining
an anonymous class. Work around is for caller to manually box the
(varargs) into an array, bypassing convenience of varargs support.

==========$ cat -n Quick.java
     1 class Quick
     2 {
     3 Quick() {
     4 Fox fox1 = new Fox(1) {}; // compiles
     5 Fox fox2 = new Fox(new String[] { "hello" }) {}; // compiles
     6
     7 // NullPointerException not thrown when following 4 lines are
     8 // commented out.
     9
    10 Fox fox3 = new Fox(null) {}; // compiles, but ambiguous?
    11 Fox fox4 = new Fox() {}; // javac NullPointerException
    12 Fox fox5 = new Fox("hello") {}; // javac NullPointerException
    13 Fox fox6 = new Fox("hello", "bye") {}; // javac NullPointerException
    14 }
    15 }
    16
    17 class Fox
    18 {
    19 Fox(int a) {
    20 _keys = new String[0];
    21 }
    22
    23 Fox(String... keys) {
    24 _keys = keys;
    25 }
    26
    27 final String[] _keys;
    28
    29 }
==========$ newjavac Quick.java
+ exec /usr/java1.5/bin/javac -J-esa -source 1.5 -target 1.5 Quick.java
An exception has occurred in the compiler (1.5.0-auto-tiger). Please file a bug at the Java Developer Connection (http://java.sun.com/cgi-bin/bugreport.cgi) after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.NullPointerException
        at com.sun.tools.javac.comp.Flow.visitNewClass(Flow.java:1105)
        at com.sun.tools.javac.tree.Tree$NewClass.accept(Tree.java:841)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:34)
        at com.sun.tools.javac.comp.Flow.scanExpr(Flow.java:500)
        at com.sun.tools.javac.comp.Flow.visitVarDef(Flow.java:725)
        at com.sun.tools.javac.tree.Tree$VarDef.accept(Tree.java:511)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:34)
        at com.sun.tools.javac.comp.Flow.scanStat(Flow.java:484)
        at com.sun.tools.javac.comp.Flow.scanStats(Flow.java:492)
        at com.sun.tools.javac.comp.Flow.visitBlock(Flow.java:732)
        at com.sun.tools.javac.tree.Tree$Block.accept(Tree.java:540)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:34)
        at com.sun.tools.javac.comp.Flow.scanStat(Flow.java:484)
        at com.sun.tools.javac.comp.Flow.visitMethodDef(Flow.java:684)
        at com.sun.tools.javac.tree.Tree$MethodDef.accept(Tree.java:482)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:34)
        at com.sun.tools.javac.comp.Flow.visitClassDef(Flow.java:624)
        at com.sun.tools.javac.tree.Tree$ClassDef.accept(Tree.java:438)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:34)
        at com.sun.tools.javac.comp.Flow.analyzeTree(Flow.java:1223)
        at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:420)
        at com.sun.tools.javac.main.Main.compile(Main.java:584)
        at com.sun.tools.javac.main.Main.compile(Main.java:536)
        at com.sun.tools.javac.Main.compile(Main.java:44)
        at com.sun.tools.javac.Main.main(Main.java:35)
==========$