docs: Remove empty string defaults from entities

distribution/index.md

@@ -626,14 +626,7 @@ Now try to add another book by issuing a `POST` request to `/books` with the fol
 }
 ```
 
-Oops, we forgot to add the title. Submit the request anyway, you should get a 500 error with the following message:
-
-> An exception occurred while executing 'INSERT INTO book [...] VALUES [...]' with params [...]:
-> SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'title' cannot be null
-
-Did you notice that the error was automatically serialized in JSON-LD and respects the Hydra Core vocabulary for errors?
-It allows the client to easily extract useful information from the error. Anyway, it's bad to get a SQL error when submitting
-a request. It means that we didn't use a valid input, and [it's a bad and dangerous practice](https://cheatsheetseries.owasp.org/cheatsheets/Input_Validation_Cheat_Sheet.html).
+The book is successfully created but there is a problem; we did not give it a title. It makes no sense to create a book record without a title so we really should have some validation measures in place to prevent this from being possible.
 
 API Platform comes with a bridge with [the Symfony Validator Component](https://symfony.com/doc/current/validation.html).
 Adding some of [its numerous validation constraints](https://symfony.com/doc/current/validation.html#supported-constraints)
@@ -654,6 +647,11 @@ Modify the following files as described in these patches:
       */
 +    #[Assert\Isbn]
      public ?string $isbn = null;
+
+      * @ORM\Column
+      */
++    #[Assert\NotBlank]
+     public string $title = '';
 
       * @ORM\Column(type="text")
       */