Building array of 'truthy' rule conditions
First up, you should really be using more modern variable definitions (using let and const instead of var).

As for your conditional processing for the mongoDB clauses, the simpler way to process the data would be to accumulate all the clauses in to a single temporary array, and then filter that array in to the actual query clause. For example, consider:

const clauses = [
    mongoRequestsHelper.getFromConditions(rule.A),
    mongoRequestsHelper.getFromConditions(rule.B),
    mongoRequestsHelper.getFromConditions(rule.C),
    mongoRequestsHelper.getFromConditions(rule.D),
    ......
];

const ruleConditions = {
    // filter out non-truthy clauses
    $and: clauses.filter(clause =&gt; clause)
};