Fixed removing entries in the new Configuration (via set(x, null))

src/main/java/org/bukkit/configuration/MemorySection.java

@@ -186,7 +186,11 @@ public class MemorySection implements ConfigurationSection {
         String key = split[split.length - 1];
 
         if (section == this) {
-            map.put(key, prepForStorage(value));
+            if (value == null) {
+                map.remove(key);
+            } else {
+                map.put(key, prepForStorage(value));
+            }
         } else {
             section.set(key, value);
         }

src/test/java/org/bukkit/configuration/ConfigurationSectionTest.java

@@ -162,7 +162,15 @@ public abstract class ConfigurationSectionTest {
         ConfigurationSection section = getConfigurationSection();
         
         section.set("exists", "hello world");
+        
+        assertTrue(section.contains("exists"));
+        assertTrue(section.isSet("exists"));
         assertEquals("hello world", section.get("exists"));
+        
+        section.set("exists", null);
+        
+        assertFalse(section.contains("exists"));
+        assertFalse(section.isSet("exists"));
     }
 
     @Test