[Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions
merged branch bschussek/issue7558 (PR #7917)

This PR was merged into the 2.1 branch.

Discussion
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[Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7558
| License       | MIT
| Doc PR        | -

Commits
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bcb5400 [Form] Fixed transform()/reverseTransform() to always throw TransformationFailedExceptions