throw NoSuchElementException instead of returning null in unchecked Iterator::next implementations

h2/src/main/org/h2/mvstore/Cursor.java

@@ -6,6 +6,7 @@
 package org.h2.mvstore;
 
 import java.util.Iterator;
+import java.util.NoSuchElementException;
 
 /**
  * A cursor to iterate over elements in ascending order.
@@ -79,7 +80,7 @@ public class Cursor<K, V> implements Iterator<K> {
     @Override
     public K next() {
         if(!hasNext()) {
-            return null;
+            throw new NoSuchElementException();
         }
         current = null;
         return last;

h2/src/main/org/h2/mvstore/db/MVSpatialIndex.java

@@ -362,7 +362,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex, MVIndex {
 
         @Override
         public boolean next() {
-            current = it.next();
+            current = it.hasNext() ? it.next() : null;
             searchRow = null;
             row = null;
             return current != null;
@@ -374,6 +374,5 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex, MVIndex {
         }
 
     }
-
 }
 

h2/src/main/org/h2/mvstore/tx/TransactionMap.java

@@ -15,6 +15,7 @@ import java.util.AbstractMap;
 import java.util.BitSet;
 import java.util.Iterator;
 import java.util.Map;
+import java.util.NoSuchElementException;
 
 /**
  * A map that supports transactions.
@@ -636,6 +637,7 @@ public class TransactionMap<K, V> {
             this.committingTransactions = committingTransactions;
 
             this.includeAllUncommitted = includeAllUncommitted;
+            fetchNext();
         }
 
         protected abstract X registerCurrent(K key, VersionedValue data);
@@ -672,19 +674,16 @@ public class TransactionMap<K, V> {
 
         @Override
         public final boolean hasNext() {
-            if(current == null) {
-                fetchNext();
-            }
             return current != null;
         }
 
         @Override
         public final X next() {
-            if(!hasNext()) {
-                return null;
+            if(current == null) {
+                throw new NoSuchElementException();
             }
             X result = current;
-            current = null;
+            fetchNext();
             return result;
         }
 

h2/src/test/org/h2/test/store/TestMVStore.java

@@ -12,6 +12,7 @@ import java.nio.charset.StandardCharsets;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.NoSuchElementException;
 import java.util.Random;
 import java.util.TreeMap;
 import java.util.concurrent.TimeUnit;
@@ -1977,7 +1978,7 @@ public class TestMVStore extends TestBase {
             assertEquals(i, it.next().intValue());
         }
         assertFalse(it.hasNext());
-        assertNull(it.next());
+        assertThrows(NoSuchElementException.class, it).next();
         for (int j = 0; j < 10; j++) {
             it = m.keyIterator(j);
             for (int i = j; i < 10; i++) {