If you want to apply conditional validation on 'Middle Name' or 'Last Name', then you need to add 'First Name' input as 'Bharat'
{{userFormGroup.controls.firstName.errors.required.message}}
Conditional Required Validation.
Conditional validation will be applied if the 'FirstName' field have value of 'Bharat'
Conditional Expression with type 'string'
{{userFormGroup.controls.lastName.errors.required.message}}
Shows Custom Validation Message.
{{userFormGroup.controls.userName.errors.required.message}}