Reflection with property decorator in typescript does not work

I'm trying to create a decorator (NonExportable) to tell which fields in a class should not be exported. Here is the code:

nonexportable-decorators.ts

const NON_EXPORTABLE_KEY = Symbol("NonExportable");

export default function NonExportable() {
   return Reflect.metadata(NON_EXPORTABLE_KEY, true);
}

export function isNonExportable (target: any, propertyKey: string): boolean {
   return Reflect.getMetadata(NON_EXPORTABLE_KEY, target, propertyKey);
}

The decorator is being used in the "personal" model, as shown below:

personaFisica.ts

import NonExportable from "../util/nonexportable-decorator"

export class Contribuinte {
    ni: string; 
    @NonExportable()    
    cpf: number;
    @NonExportable()    
    cnpjEstabelecimento: number;
}

However, apparently is not being recorded anything in metadata, considering that when running the Reflect.isNonExportable is returned a value undefined . That way, it is always returned false by isNonExportable . What am I doing wrong?