FIX [Form][FormTypeGuesserChain] Replace reading of private property on 'getter' method call. Realize 'getter' method

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        |