Correctly resize integer map (#2422)

src/main/java/com/comphenix/protocol/collections/IntegerMap.java

@@ -76,8 +76,7 @@ public class IntegerMap<T> {
 
         // Fast calculation of the new size.
         // See IntMath#ceilingPowerOfTwo in newer guava versions.
-        int newLength = IntegerMath.nextPowerOfTwo(key);
-
+        int newLength = IntegerMath.nextPowerOfTwo(key + 1);
         this.array = Arrays.copyOf(array, newLength);
     }
 

src/test/java/com/comphenix/protocol/collections/IntegerMapTest.java

@@ -0,0 +1,23 @@
+package com.comphenix.protocol.collections;
+
+import com.comphenix.protocol.utility.IntegerMath;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class IntegerMapTest {
+    @Test
+    public void testNextPower() {
+        assertEquals(128, IntegerMath.nextPowerOfTwo(127));
+        assertEquals(128, IntegerMath.nextPowerOfTwo(128));
+        assertEquals(256, IntegerMath.nextPowerOfTwo(129));
+    }
+    @Test
+    public void testCapacityIncrement() {
+        IntegerMap<Boolean> map = new IntegerMap<>();
+        for (int i = 0; i < 512; i++) {
+            map.put(i, false);
+        }
+        assertEquals(map.size(), 512);
+    }
+}