[Bleeding] Removing the last metadata item for a key now sets hasMetadata(key) to false. Addresses BUKKIT-1380

By: rmichela <deltahat@gmail.com>

paper-api/src/main/java/org/bukkit/metadata/MetadataStoreBase.java

@@ -86,6 +86,9 @@ public abstract class MetadataStoreBase<T> {
         for (int i = 0; i < metadataList.size(); i++) {
             if (metadataList.get(i).getOwningPlugin().equals(owningPlugin)) {
                 metadataList.remove(i);
+                if (metadataList.isEmpty()) {
+                    metadataMap.remove(key);
+                }
             }
         }
     }

paper-api/src/test/java/org/bukkit/metadata/MetadataStoreTest.java

@@ -96,6 +96,15 @@ public class MetadataStoreTest {
         assertEquals(20, subject.getMetadata("subject", "key").get(0).value());
     }
 
+    @Test
+    public void testMetadataRemoveLast() {
+        subject.setMetadata("subject", "key", new FixedMetadataValue(pluginX, 10));
+        subject.removeMetadata("subject", "key", pluginX);
+
+        assertFalse(subject.hasMetadata("subject", "key"));
+        assertEquals(0, subject.getMetadata("subject", "key").size());
+    }
+
     @Test
     public void testMetadataRemoveForNonExistingPlugin() {
         subject.setMetadata("subject", "key", new FixedMetadataValue(pluginX, 10));