Allow passing empty indices list to CreateTableOperation (aws#3923)

* CreateTableRequest cannot handle empty list of indices of any type. It
  throws exception when given such a list. At the same time, it nicely
  handles the cases when indices lists are null. Make sure then that
  when empty indices list is passed CreateTableOperation, then in the
  CreateTableRequest it's just reflected as null.

Author: breader124

services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/operations/CreateTableOperation.java

@@ -74,7 +74,7 @@ public CreateTableRequest generateRequest(TableSchema<T> tableSchema,
         List<software.amazon.awssdk.services.dynamodb.model.GlobalSecondaryIndex> sdkGlobalSecondaryIndices = null;
         List<software.amazon.awssdk.services.dynamodb.model.LocalSecondaryIndex> sdkLocalSecondaryIndices = null;
 
-        if (this.request.globalSecondaryIndices() != null) {
+        if (this.request.globalSecondaryIndices() != null && !this.request.globalSecondaryIndices().isEmpty()) {
             sdkGlobalSecondaryIndices =
                 this.request.globalSecondaryIndices().stream().map(gsi -> {
                     String indexPartitionKey = tableSchema.tableMetadata().indexPartitionKey(gsi.indexName());
@@ -92,7 +92,7 @@ public CreateTableRequest generateRequest(TableSchema<T> tableSchema,
                 }).collect(Collectors.toList());
         }
 
-        if (this.request.localSecondaryIndices() != null) {
+        if (this.request.localSecondaryIndices() != null && !this.request.localSecondaryIndices().isEmpty()) {
             sdkLocalSecondaryIndices =
                 this.request.localSecondaryIndices().stream().map(lsi -> {
                     Optional<String> indexSortKey = tableSchema.tableMetadata().indexSortKey(lsi.indexName());