/* package whatever; // don't place package name! */
 
import java.util.*;
import java.util.concurrent.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		try {
		ConcurrentHashMap<String, String> m = new ConcurrentHashMap<String, String>();
		m.replace("nokey", null, "noval");
		System.out.println(m.get("nokey") == null ? "null" : "not null");
 
		} catch(Exception e) {
			System.out.println(e);	
		}
	}
}

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