fix after review

Author: zstan

modules/catalog/src/main/java/org/apache/ignite/internal/catalog/commands/CreateSchemaCommand.java

@@ -49,8 +49,14 @@ public class CreateSchemaCommand implements CatalogCommand {
     private CreateSchemaCommand(String schemaName, boolean ifNotExists, boolean systemSchemaCommand) {
         validateIdentifier(schemaName, "Name of the schema");
 
-        if (systemSchemaCommand && !CatalogUtils.isSystemSchema(schemaName)) {
-            throw new CatalogValidationException(format("Not a system schema, schema: '{}'", schemaName));
+        if (systemSchemaCommand) {
+            if (!CatalogUtils.isSystemSchema(schemaName)) {
+                throw new CatalogValidationException(format("Not a system schema, schema: '{}'", schemaName));
+            }
+        } else {
+            if (CatalogUtils.isSystemSchema(schemaName)) {
+                throw new CatalogValidationException("Reserved system schema with name '{}' can't be created.", schemaName);
+            }
         }
 
         this.schemaName = schemaName;