Indeed, if a Java Map implementation allows for null values, then it is possible for the Map to return its value for the given key, but that value might be a null.

Cannot Assume Serializability for Java Map’s Nested Classes. how-to. Oct 23, 2010 7 mins. Software Development.

The free Java applet MAPresso generates choropleth maps, informational maps that represent statistical variations with shaded colors. You've seen them used to display voting statistics ...