CNDB-12774: Not index empty non-literal values (#1556)

Also, prevent encoding error when searching empty varint and decimal values

Author: adelapena

src/java/org/apache/cassandra/index/sai/disk/v1/SSTableIndexWriter.java

@@ -240,7 +240,7 @@ else if (shouldFlush(sstableRowId))
             currentBuilder = newSegmentBuilder(sstableRowId);
         }
 
-        if (term.remaining() == 0 && !indexContext.getValidator().allowsEmpty())
+        if (term.remaining() == 0 && TypeUtil.skipsEmptyValue(indexContext.getValidator()))
             return;
 
         long allocated = currentBuilder.addAll(term, type, key, sstableRowId);

src/java/org/apache/cassandra/index/sai/memory/TrieMemtableIndex.java

@@ -168,7 +168,7 @@ public ByteBuffer getMaxTerm()
     @Override
     public void index(DecoratedKey key, Clustering clustering, ByteBuffer value, Memtable memtable, OpOrder.Group opGroup)
     {
-        if (value == null || (value.remaining() == 0 && !validator.allowsEmpty()))
+        if (value == null || (value.remaining() == 0 && TypeUtil.skipsEmptyValue(validator)))
             return;
 
         RequestSensors sensors = requestTracker.get();

src/java/org/apache/cassandra/index/sai/utils/TypeUtil.java

@@ -278,8 +278,8 @@ else if (isBigDecimal(type))
      */
     public static ByteBuffer asIndexBytes(ByteBuffer value, AbstractType<?> type)
     {
-        if (value == null)
-            return null;
+        if (value == null || value.remaining() == 0)
+            return value;
 
         if (isInetAddress(type))
             return encodeInetAddress(value);
@@ -649,6 +649,14 @@ public static boolean isComposite(AbstractType<?> type)
         return type instanceof CompositeType;
     }
 
+    /**
+     * @return {@code true} if the empty values of the given type should be excluded from indexing, {@code false} otherwise.
+     */
+    public static boolean skipsEmptyValue(AbstractType<?> type)
+    {
+        return !type.allowsEmpty() || !isLiteral(type);
+    }
+
     /**
      * @return base type if given type is reversed, otherwise return itself
      */