possibly fixes #15

The error will have to do with PR #14. As I am still very limited in time, I gave it a shot with this fix, please try if it works now for you.
Otherwise maybe @wmattei could have a look at it? Also a repro would help, as I cannot reproduce it here.
Cheers!

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ng-mat-search-bar",
-  "version": "3.2.0",
+  "version": "3.2.1",
   "license": "MIT",
   "scripts": {
     "build": "ng build",

src/app/ng-mat-search-bar/mat-search-bar/mat-search-bar.component.html

@@ -4,7 +4,7 @@
 </mat-form-field>
 
 <!-- FORM CONTROL WAY -->
-<mat-form-field class="mat-search_field" [@slideInOut]="searchVisible">
+<mat-form-field *ngIf="formControl" class="mat-search_field" [@slideInOut]="searchVisible">
   <input #input matInput type="text" placeholder="" [formControl]="formControl" (blur)="onBlurring(input.value)"
     (keyup.enter)="onEnterring(input.value)" (focus)="onFocussing(input.value)" />
 </mat-form-field>
@@ -13,4 +13,4 @@
 <span class="mat-search_icons" [class.mat-search_icons--active]="searchVisible">
   <mat-icon class="mat-search_icon-close" (click)="close()" matRipple>close</mat-icon>
   <mat-icon class="mat-search_icon-search" (click)="open()" matRipple>search</mat-icon>
-</span>
+</span>