Apply suggestions from code review

Co-authored-by: Toshihiro Suzuki <[email protected]>

Author: KodaiD

core/src/main/java/com/scalar/db/storage/jdbc/JdbcAdmin.java

@@ -890,8 +890,8 @@ public void renameColumn(
       throws ExecutionException {
     try {
       TableMetadata currentTableMetadata = getTableMetadata(namespace, table);
-      rdbEngine.throwIfRenameColumnNotSupported(oldColumnName, currentTableMetadata);
       assert currentTableMetadata != null;
+      rdbEngine.throwIfRenameColumnNotSupported(oldColumnName, currentTableMetadata);
       TableMetadata.Builder tableMetadataBuilder =
           TableMetadata.newBuilder(currentTableMetadata).renameColumn(oldColumnName, newColumnName);
       if (currentTableMetadata.getPartitionKeyNames().contains(oldColumnName)) {

core/src/main/java/com/scalar/db/storage/jdbc/RdbEngineStrategy.java

@@ -273,7 +273,7 @@ default void throwIfDuplicatedIndexWarning(SQLWarning warning) throws SQLExcepti
   }
 
   /**
-   * Throws an exception if renaming columns is not supported in the underlying database.
+   * Throws an exception if renaming the column is not supported in the underlying database.
    *
    * @param columnName the current name of the column to rename
    * @param tableMetadata the current table metadata