driver-core/src/main/com/mongodb/client/model/Updates.java
public static Bson mul(final String fieldName, final Number number) {
        notNull("number", number);
        return new SimpleUpdate<Number>(fieldName, number, "$mul");
    }
public static Bson mul(final String fieldName, final Number number) {
        notNull("number", number);
        return new SimpleUpdate<Number>(fieldName, number, "$mul");
    }
Creates an update that multiplies the value of the field with the given name by the given number.

@param fieldName the non-null field name
@param number    the non-null number
@return the update
@mongodb.driver.manual reference/operator/update/mul/ $mul