Wappler extension number input doesn't work

Wappler version: 5.0.0 beta 2 (also happens with 4.9.1)
NodeJS

The following property in HJSON of a Wappler extension:

{ name: 'chunkSize', optionName:'chunkSize', title: 'Chunk size', type: 'number', required: false, defaultValue :300, serverDataBindings: true,  help: 'The number of rows to insert/update at once'},

The number is not saved, becomes an empty string in the server action JSON:

"chunkSize": ""