Fix inconsistent null handling between array and single object version RAM estimation

lucene/CHANGES.txt

@@ -162,6 +162,9 @@ Optimizations
 
 Bug Fixes
 ---------------------
+* Fix missing null check in RamUsageEstimator.sizeOf(Accountable) to be consistent
+  with sizeOf(String) and sizeOf(Accountable[]). (Tim Grein)
+
 * GITHUB#14049: Randomize KNN codec params in RandomCodec. Fixes scalar quantization div-by-zero
   when all values are identical. (Mike Sokolov)
 

lucene/core/src/java/org/apache/lucene/util/RamUsageEstimator.java

@@ -428,6 +428,9 @@ private static long sizeOfObject(Object o, int depth, long defSize) {
    * Accountable#ramBytesUsed()} method.
    */
   public static long sizeOf(Accountable accountable) {
+    if (accountable == null) {
+      return 0;
+    }
     return accountable.ramBytesUsed();
   }
 

lucene/core/src/test/org/apache/lucene/util/TestRamUsageEstimator.java

@@ -150,6 +150,11 @@ public void testMap() {
     assertEquals((double) actual, (double) estimated, (double) actual * errorFactor);
   }
 
+  public void testAccountable() {
+    assertEquals(0L, RamUsageEstimator.sizeOf((Accountable) null));
+    assertEquals(1L, RamUsageEstimator.sizeOf(new DummyAccountable()));
+  }
+
   public void testCollection() {
     List<Object> list = new ArrayList<>();
     list.add(1234L);
@@ -252,4 +257,11 @@ private static class HolderSubclass extends Holder {
   private static class HolderSubclass2 extends Holder {
     // empty, only inherits all fields -> size should be identical to superclass
   }
+
+  private static class DummyAccountable implements Accountable {
+    @Override
+    public long ramBytesUsed() {
+      return 1L;
+    }
+  }
 }