Field placeholder is not displayed react-query-builder

I'm using react-query-builder library. But when I add a rule, the place holder label is not displayed.

(blue field) no text is shown

I would like to show a label like "Select an option". Here is part of the config JSON, where I add the fieldPlaceholder

"fieldLabel": "Field",
"operatorLabel": "Operator",
"funcLabel": "Function",
"fieldPlaceholder": "Select field",

Any ideas why is this happening?