import { Operator } from './operator';
import { Query } from '../query/query';
import { Operators } from './operators';
/**
 * An operator that can be used on any field and matches entries with null or empty string values.
 *
 * Beware that if any additional constraints should be applied to the generated query the results may behave strangely.
 * Consult the [createQueryWithConstraint()]{@link IsNull#createQueryWithConstraint} method for more information.
 */
export declare class IsNull extends Operator<any> {
    constructor();
    /**
     * @param elasticKeywords the queried fields
     * @returns Generates a query that matches null fields and fields with empty string values.
     */
    createQuery(elasticKeywords: Array<string>): Query;
    /**
     * Counterintuitively elasticsearch query string queries behave weirdly when combining the queries with operators such as `AND`.
     * Because of this the following query:
     *
     *    (dataSet.text_0.value:"")
     *
     * returns an empty result set.
     *
     * But query that should be intuitively more constraining:
     *
     *     (dataSet.text_0.value:"") AND (processId:600168ccf68fea5241ae5e62)
     *
     * will return a non empty and expected result.
     *
     * This method exists to combat this issue and add the, sometimes necessary, constraint into the query generated by this operator.
     *
     * @param elasticKeywords the queried fields
     * @param constraint a constraining query that is distributively applied into the query generated by this operator.
     * If an empty query is provided the result will be the same as calling [createQuery()]{@link IsNull#createQuery}.
     * @returns a query with distributively applied constraint query
     */
    createQueryWithConstraint(elasticKeywords: Array<string>, constraint: Query): Query;
    /**
     * @param elasticKeyword the queried field
     * @returns a string representation of the query that checks whether the field is null
     */
    protected nullQueryString(elasticKeyword: string): string;
    /**
     * @param elasticKeyword the queried field
     * @returns a string representation of the query that checks whether the field has an empty string value
     */
    protected emptyStringQueryString(elasticKeyword: string): string;
    getOperatorNameTemplate(): Array<string>;
    serialize(): Operators | string;
}