FULL PRODUCT VERSION :
Tested on both Java5 and Java6

$ java -version
java version "1.6.0_05"
Java(TM) SE Runtime Environment (build 1.6.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 10.0-b19, mixed mode)

$ java -version
java version "1.5.0_15"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_15-b04)
Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_15-b04, mixed mode)



ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 5.2.3790]
(running in a Cygwin shell)

A DESCRIPTION OF THE PROBLEM :
When using the ternary operator (conditional assignment) generics are not
properly handled. This code gives an error

import java.util.*;
public class TestGenerics {
    public static void main(String[] args) throws Exception {
        boolean b = true;
        List<String> list = b
            ? Collections.emptyList()
            : Collections.emptyList();
    }
}

$ javac TestGenerics.java
TestGenerics.java:6: incompatible types
found : java.util.List<java.lang.Object>
required: java.util.List<java.lang.String>
            ? Collections.emptyList()

On the other hand this works

        List<String> list = null;
        if (b)
            list = Collections.emptyList();
        else
            list = Collections.emptyList();

I don't see why these should be different.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the above code with javac from JDK 1.6.0

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Code should be valid
ACTUAL -
$ javac TestGenerics.java
TestGenerics.java:6: incompatible types
found : java.util.List<java.lang.Object>
required: java.util.List<java.lang.String>
            ? Collections.emptyList()

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;
public class TestGenerics {
    public static void main(String[] args) throws Exception {
        boolean b = true;
        List<String> list = b
            ? Collections.emptyList()
            : Collections.emptyList();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use if/else