title: Cannot read property 'toString' of undefined
body: <p>data-filter.pipe.ts</p>
  
  <pre><code>import { Pipe, PipeTransform } from '@angular/core';
  
  @Pipe({
    name: 'dataFilter'
  })
  export class DataFilterPipe implements PipeTransform {
  
    transform(array: any[], query: string): any {
  
      if (!query || query === '') {
        return array;
      }
  
      let filtered = [];
      array.forEach(function (element) {
        let isAdded = false;
        Object.keys(element).forEach(function (key, index) {
          if (!isAdded &amp;&amp; element[key].toString().toLowerCase().includes(query.toLowerCase())) {
            filtered.push(element);
            isAdded = true;
          }
        });
      });
  
      return filtered;
    }
  
  }
  </code></pre>
  
  <p>in .html</p>
  
  <pre><code>&lt;table class="bordered table-bordered" [mfData]="users | dataFilter : filterQuery" #mf="mfDataTable"
  </code></pre>