mdbModal gives an error

Dear supporter,

We are using mdbModal for displaying some messages. However we get the following error:

TypeError: Cannot read property 'backdrop' of undefined
AppComponent.html:37
message:"Cannot read property 'backdrop' of undefined"
ngDebugContext:DebugContext_ {view: Object, nodeIndex: 15, nodeDef: Object, …}
ngErrorLogger:function () { … }
stack:"TypeError: Cannot read property 'backdrop' of undefinedn at ModalDirective.showBackdrop (webpack-internal:///../../../../ng-mdb-pro/free/modals/modal.directive.ts:213:42)n at ModalDirective.show (webpack-internal:///../../../../ng-mdb-pro/free/modals/modal.directive.ts:122:14)n at ActivityCreateComponent.set [as show] (webpack-internal:///../../../../../src/app/activity-create/activity-create.component.ts:110:41)n at updateProp (webpack-internal:///../../../core/esm5/core.js:12826:37)n at checkAndUpdateDirectiveInline (webpack-internal:///../../../core/esm5/core.js:12533:19)n at checkAndUpdateNodeInline (webpack-internal:///../../../core/esm5/core.js:14100:20)n at checkAndUpdateNode (webpack-internal:///../../../core/esm5/core.js:14043:16)n at debugCheckAndUpdateNode (webpack-internal:///../../../core/esm5/core.js:14936:76)n at debugCheckDirectivesFn (webpack-internal:///../../../core/esm5/core.js:14877:13)n at Object.eval [as updateDirectives] (ng:///AppModule/AppComponent.ngfa...
__proto__:Error {constructor: , name: "TypeError", message: "", …}

We look into the code and  see that it uses "this.config.backdrop" when this.config is undefined.

rule 259 of modal.directive.ts

if (this._isShown && this.config.backdrop && (!this.backdrop || !this.backdrop.instance.isShown)) {

Is it a well-known error?

Regards,

Duong