backport of #2232 (issue 418)

Author: l-trotta

output/schema/schema.json

@@ -96,9 +96,9 @@ export class PathHierarchyTokenizer extends TokenizerBase {
 
 export class PatternTokenizer extends TokenizerBase {
   type: 'pattern'
-  flags: string
-  group: integer
-  pattern: string
+  flags?: string
+  group?: integer
+  pattern?: string
 }
 
 export class StandardTokenizer extends TokenizerBase {