Angular 2+ reactive form validation - either this or that -

i have 3 field form - first name, last name, id number - want set user must either enter data 2 name fields or enter id number form valid , "submittable".

my code

ngoninit() {     this.person = this.fb.group({       'fname': [],       'lname': [],       'certid': []     },{       validator:(formgroup:formgroup)=>{         return this.validateinput(formgroup);         }       }     );   }    validateinput(formgroup:formgroup){     if(formgroup.controls["fname"].value && formgroup.controls["lname"].value || formgroup.controls["certid"].value){       console.log('ok');       return {validateinputdata:true};       }       else {         console.log('not ok');       return null;       }   } 

while validation runs when form/page loaded , generates 'fail'('not ok'), submit button nevertheless active:

<button type="submit" class="btn btn-success"  [disabled]="submitpending || person.invalid"> submit<span *ngif="submitpending" class="glyphicon glyphicon-refresh glyphicon-refresh-animate"></span> </button> 

where going wrong?

are return statements backwards?

return null when ok , error when not ok.

if((formgroup.controls["fname"].value && formgroup.controls["lname"].value)                 || formgroup.controls["certid"].value){   console.log('ok');   return null;   }   else {     console.log('not ok');     return {validateinputdata: true};   } 

the 'validateinputdata' property name of error in errors collection.