Angular. Problem with custom validator

I have a field that requires conditional validation.

If a certain dropdown value is chosen then I need the field to be required.  No problem with one field and custom validator.  Unfortunately its email field and I have to add pattern and standard email validators too and this is causing me a nightmare to implement.

Currently the following works for required:

  
 proofEmail: ['',conditionalValidator( (()=> this.isProofPDF === true),Validators.required)],

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My conditionalValidator function here:

function conditionalValidator(condition: (()=> boolean), validator : ValidatorFn): ValidatorFn {
  return (control : AbstractControl):{[key:string]:any} => {
    if(! condition()){
      return null;
    }
    return validator(control);
  }

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My html here:

 <input class="form-control" formControlName='proofEmail' id="proof-email">

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So Im simply trying to add validators.email and validators.pattern(mypattern) 

here

 but no matter what I try I cant get it right.  When I add validators at runtime i have a different set of issues.  Hope someone can help.