ADDITIONAL SYSTEM INFORMATION :
OS X but likely all.

A DESCRIPTION OF THE PROBLEM :
If you execute a lambda in computeIfPresent method that in turn calls computeIfPresent inside itself with a lambda that returns null and after completion returns null.

Then try to put a value into the map the size will be zero.
This is a bit messy description see "Steps to Reproduce" where I have added some code to reproduce this issue.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Class that reproduces this error and throws and exception if error is found.
====== ConcurrentHashMapTest.java ======

import java.lang.IllegalStateException;
import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapTest {

public static void main(final String[] args)
{
final ConcurrentHashMap<String, String> concurrentHashMap = new ConcurrentHashMap<>();

final String key = "key";
final String value = "value";

System.out.println("Put called with key=" + key + ", value=" + value + ".");
concurrentHashMap.put(key, value);

System.out.println("ConcurrentHashMap size=" + concurrentHashMap.size() + ".");

System.out.println("Running nested computeIdPresent with null return");
concurrentHashMap.computeIfPresent(key, (aKey, aValue) -> {
concurrentHashMap.computeIfPresent(key, (bKey, bValue) -> {
return null;
});
return null;
});

System.out.println("ConcurrentHashMap size=" + concurrentHashMap.size() + ".");

System.out.println("Put called with key=" + key + ", value=" + value + ".");
concurrentHashMap.put(key, value);

final int mapSize = concurrentHashMap.size();
final int expectedSize = 1;

System.out.println("ConcurrentHashMap size=" + mapSize + ".");
if (expectedSize != mapSize) {
throw new IllegalStateException("Expected map to have size of value 1 after put operation.");
}
}
}



CUSTOMER SUBMITTED WORKAROUND :
Refactor call to computeIfPresent lambda.

FREQUENCY : always