[editor] Fix answer scheme for complex radio button group

projects/common/models/elements/input-elements/radio-button-group-complex.ts

@@ -54,7 +54,7 @@ export class RadioButtonGroupComplexElement extends InputElement
       type: 'integer',
       format: '',
       multiple: false,
-      nullable: !this.value && this.value !== 0,
+      nullable: false,
       values: this.getAnswerSchemeValues(),
       valuesComplete: true
     };