graphqlExpress(async req => {
    // console.log(req.query)
    try {
        ...
        customOptions.schema = MergeSchemas(userContext.role);
        // context can accept a function returning the context object
        const context =
            typeof options.context === 'function'
                ? await options.context(userContext)
                : { ...options.context, ...userContext };
        // return the configured options to be used by the graphql server
        // console.log(customOptions)
        console.log(customOptions.schema)
        ...

export const MergeSchemas = role => {
    const typeDefs = [accountsTypeDefs, bidsTypeDefs, goodsTypeDefs, commonGoodsTypeDefs, commonBidsTypeDefs];
    let resolvers = accountsResolvers;
    if (role) {
        if (role == Users.ROLE_CLIENT()) {

            typeDefs.push(customerGoodsTypeDefs)
            typeDefs.push(customerBidsTypeDefs)
            resolvers = merge(resolvers, clientGoodsResolvers, customerBidsResolvers)
        }
        if (role == Users.ROLE_BROKER()) {
            typeDefs.push(brokerBidsTypeDefs)
            resolvers = merge(resolvers, brokerBidsResolvers)
        }
    }
    console.log(resolvers)

    return makeExecutableSchema({
        typeDefs,
        resolvers,
    });
}

Error: Expected undefined to be a GraphQL schema.