Cannot read property 'toString' of null when searc

Hello I getting these errors when i start typing in the search box:

task-queue.component.html:3 ERROR TypeError: Cannot read property 'toString' of null
at mdb-table-editor.js:309
at Array.some (<anonymous>)
at mdb-table-editor.js:304
at Array.filter (<anonymous>)
at MdbTableEditorDirective.push../node_modules/mdb-table-editor/fesm5/mdb-table-editor.js.MdbTableEditorDirective.filterIterableArray (mdb-table-editor.js:299)
at MdbTableEditorDirective.push../node_modules/mdb-table-editor/fesm5/mdb-table-editor.js.MdbTableEditorDirective.performSearch (mdb-table-editor.js:336)
at Object.updateDirectives (task-queue.component.html:3)
at Object.debugUpdateDirectives [as updateDirectives] (core.js:23911)
at checkAndUpdateView (core.js:23307)
at callViewAction (core.js:23548)

My Component TS:

@ViewChild('tableTasks') mdbTableEditor: MdbTableEditorDirective;
modalRef: MDBModalRef;
editTaskForm: FormGroup;
headElements = ['ID', 'Předmět', 'Zadání', 'Termín', 'Kategorie', 'Status', 'Ticket', 'Řešitel', 'Zadavatel'];
visibleItems = 10;
searchTaskText = '';
ngOnInit() {
    this.elements = this.route.snapshot.data['queue'];
    this.elements.map((task: Task, index) => {
        this.task_time = [];
        if (!task.finished_at) {
            const deadline = new Date(task.deadline);
            const createdate = new Date(task.created_date);
            const currentdate = new Date();

            const full_diff = Math.abs(createdate.getTime() - deadline.getTime());
            const due_diff = Math.abs(currentdate.getTime() - deadline.getTime());

            const full_diffDays = Math.ceil(full_diff / (1000 * 3600 * 24));
            const full_diffHrs = Math.floor((full_diff % (1000 * 3600 * 24)) / 3600000);
            const full_diffMins = Math.round(((full_diff % (1000 * 3600 * 24)) % 3600000) / 60000);

            const due_diffDays = Math.ceil(due_diff / (1000 * 3600 * 24));
            const due_diffHrs = Math.floor((due_diff % (1000 * 3600 * 24)) / 3600000);
            const due_diffMins = Math.round(((due_diff % (1000 * 3600 * 24)) % 3600000) / 60000);
            if (currentdate < deadline) {
                const percentage = (((full_diff - due_diff) * 100) / full_diff);
                this.elements[index].task_time = {
                    percentage: percentage,
                    time_fond: full_diffDays + ' dnů, ' + full_diffHrs + ' hodin, ' + full_diffMins + ' minut',
                    due: due_diffDays + ' dnů, ' + due_diffHrs + ' hodin, ' + due_diffMins + ' minut',
                    overdue: false
                }
            } else {
                this.elements[index].task_time = {
                    percentage: 100,
                    time_fond: full_diffDays + ' dnů, ' + full_diffHrs + ' hodin, ' + full_diffMins + ' minut',
                    due: false,
                    overdue: due_diffDays + ' dnů, ' + due_diffHrs + ' hodin, ' + due_diffMins + ' minut'
                }
            }
        } else {
            const deadline = new Date(task.deadline);
            const createdate = new Date(task.created_date);
            const finishdate = new Date(task.finished_at);

            const full_diff = Math.abs(createdate.getTime() - deadline.getTime());
            const due_diff = Math.abs(finishdate.getTime() - deadline.getTime());

            const full_diffDays = Math.ceil(full_diff / (1000 * 3600 * 24));
            const full_diffHrs = Math.floor((full_diff % (1000 * 3600 * 24)) / 3600000);
            const full_diffMins = Math.round(((full_diff % (1000 * 3600 * 24)) % 3600000) / 60000);

            const due_diffDays = Math.ceil(due_diff / (1000 * 3600 * 24));
            const due_diffHrs = Math.floor((due_diff % (1000 * 3600 * 24)) / 3600000);
            const due_diffMins = Math.round(((due_diff % (1000 * 3600 * 24)) % 3600000) / 60000);
            if (finishdate < deadline) {
                const percentage = (((full_diff - due_diff) * 100) / full_diff);
                this.elements[index].task_time = {
                    percentage: percentage,
                    time_fond: full_diffDays + ' dnů, ' + full_diffHrs + ' hodin, ' + full_diffMins + ' minut',
                    due: due_diffDays + ' dnů, ' + due_diffHrs + ' hodin, ' + due_diffMins + ' minut',
                    overdue: false
                }
            } else {
                this.elements[index].task_time = {
                    percentage: 100,
                    time_fond: full_diffDays + ' dnů, ' + full_diffHrs + ' hodin, ' + full_diffMins + ' minut',
                    due: false,
                    overdue: due_diffDays + ' dnů, ' + due_diffHrs + ' hodin, ' + due_diffMins + ' minut'
                }
            }
        }
        console.log(task);
    });
    console.log(this.elements);
    this.mdbTableEditor.dataArray = this.elements;

    this.editTaskForm = this.formBuilder.group({
        taskSolver: ['', Validators.required],
        taskSubject: ['', Validators.compose([Validators.required, Validators.minLength(2), Validators.maxLength(100)])],
        taskMaintask: ['', Validators.required],
        taskDeadlineDate: ['', Validators.required],
        taskDeadlineTime: ['', Validators.required]
    });
    this.editTaskForm.get('taskSolver').valueChanges.subscribe((user_id) => {
        this.userService.getUser(user_id).subscribe((data: any) => {
            this.solver = data;
        }, error => {
            console.log(error);
        });
        console.log(this.solver);
    });
}

My Component HTML:

<div class="row">
<div class="col-md-12 mx-auto my-2">
    <div class="row w-100 d-flex justify-content-between mx-auto">
        <div class="col-md-3 d-flex align-items-center">
            <span class="font-weight-bolder">Zobrazit</span>

            <select class="browser-default custom-select mx-2" [(ngModel)]="visibleItems"
                    (ngModelChange)="visibleItems = +$event" style="width: unset;">
                <option value="10" selected>10</option>
                <option value="25">25</option>
                <option value="50">50</option>
                <option value="100">100</option>
            </select>

            <span class="font-weight-bolder">záznamů</span>
        </div>

        <div class="col-md-6 md-form my-1 text-right d-flex justify-content-between align-items-center">
            <input mdbInput type="search" class="form-control form-control-sm ml-2" [(ngModel)]="searchTaskText">
            <label class="font-weight-bolder mb-0">Hledat: </label>

        </div>
    </div>
    <table mdbTableEditor class="table table-striped z-depth-1" [itemsPerPage]="visibleItems"
           #tableTasks="mdbEditor"
           (rowHighlight)="highlightedTaskRow = $event">
        <thead>
        <tr>
            <th
                    *ngFor="let head of headElements; let i = index"
                    scope="col"
                    [mdbTableSort]="tableTasks.dataArray" [sortBy]="headElements[i]"
            >{{head | titlecase}}
                <mdb-icon fas icon="sort" class="ml-1"></mdb-icon>
            </th>
        </tr>
        </thead>
        <tbody id="mdbEditor-TableTaskBody">
        <tr *ngFor="let item of tableTasks.performSearch(this.searchTaskText); let i = index">
            <td>{{item.id}}</td>
            <td>
                {{item.subject}}<br/>
                <mdb-badge *ngIf="item.finished_at" pill="true" success="true" class="ml-1">dokončeno</mdb-badge>
                <mdb-badge *ngIf="!item.finished_at && !item.deleted_date" pill="true" warning="true" class="ml-1">
                    ve frontě
                </mdb-badge>
                <mdb-badge *ngIf="!item.task_time.due && !item.deleted_date" pill="true" danger="true" class="ml-1">
                    po termínu
                </mdb-badge>
                <mdb-badge *ngIf="item.deleted_date" pill="true" danger="true" class="ml-1">smazáno
                    (dne: {{item.deleted_date | date:'dd.MM.yyyy HH:mm'}})
                </mdb-badge>
            </td>
            <td>{{item.maintask | truncateText: 300}}</td>
            <td>{{item.deadline | date:'dd.MM.yyyy HH:mm'}}</td>
            <td *ngIf="item.tasks_category">{{item.tasks_category.name}}</td>
            <td *ngIf="item.status">{{item.status.name}}</td>
            <td *ngIf="item.ticket"><a routerLink="/tickets/{{item.ticket.id}}">{{item.ticket.subject}}</a></td>
            <td *ngIf="!item.tasks_category">TEST</td>
            <td *ngIf="!item.status">TEST</td>
            <td *ngIf="!item.ticket"></td>
            <td>
                <img src="assets/img{{item.solver.personalphoto}}"
                     class="img-fluid rounded-circle img-responsive avatar-xs mr-1"
                     alt="profilový obrázek"/>{{item.solver.firstname}} {{item.solver.secondname}}
            </td>
            <td>
                <img src="assets/img{{item.creator.personalphoto}}"
                     class="img-fluid rounded-circle img-responsive avatar-xs mr-1"
                     alt="profilový obrázek"/>{{item.creator.firstname}} {{item.creator.secondname}}
            </td>
            <td><a routerLink="/tasks/detail/{{item.id}}">
                <mdb-icon far icon="search"></mdb-icon>
            </a></td>
        </tr>
        </tbody>
        <tfoot>
        <tr>
            <td colspan="9">
                <div class="d-flex flex-center">
                    <span>Zobrazuji {{tableTasks.paginationInfo.firstItem}}
                        až {{tableTasks.paginationInfo.lastItem}}
                        z {{tableTasks.paginationInfo.allItems}} záznamů</span>
                    <div class="flex-1"></div>
                    <mdb-icon fas icon="angle-left" size="lg" (click)="tableTasks.prevPage()" class="p-2"
                              [ngClass]="{'disabled text-muted': tableTasks.disablePrevious()}"
                              mdbWavesEffect></mdb-icon>
                    <mdb-icon fas icon="angle-right" size="lg" (click)="tableTasks.nextPage()" class="p-2"
                              [ngClass]="{'disabled text-muted': tableTasks.disableNext()}"
                              mdbWavesEffect></mdb-icon>
                </div>
            </td>
        </tr>
        </tfoot>
    </table>
</div>

Can you help me?

THX. JR JON.CZ s.r.o.