[📚 docs] Add a truth table for error handling (#6100)

* Add a truth table

* hopefully more readable

* try to format better

Author: martinbonnin

docs/source/essentials/errors.mdx

@@ -4,12 +4,17 @@ title: Error handling
 
 <Note>
 
-Starting with version 4.0.0, Apollo Kotlin offers a way to handle errors automatically at parsing time. Fields that are nullable only for error purposes can also be generated as non-null in Kotlin. Read ["handling nullability"](../advanced/nullability) for more details.
+Starting with version 4.0.0, Apollo Kotlin offers a way to handle errors automatically at parsing time. Fields that are nullable only for error purposes can also be generated as non-null in Kotlin. You can read more about it in the ["handling nullability" page](../advanced/nullability).
 
 </Note>
 
 ## `ApolloResponse` 
 
+`ApolloResponse` contains three important fields:
+* `exception` contains the fetch error if any.
+* `errors` contains the GraphQL errors if any.
+* `data` contains the returned (potentially partial) data if any.
+
 Use `ApolloResponse.data` to check if the server returned data:
 
 ```kotlin
@@ -137,3 +142,16 @@ For an example, it is possible for a person to not have a starship:
 ```
 
 In that case, `starship` is a true null and not an error.
+
+## Truth table
+
+| exception | data      | errors    | meaning                                                                     |
+|-----------|-----------|-----------|-----------------------------------------------------------------------------|
+| `null`    | `null`    | `null`    | Non-compliant server, if `data` is null, there should be at least one error |
+| `null`    | `null`    | `present` | A GraphQL request error happened or a Graph field error bubbled up.         |
+| `null`    | `present` | `null`    | Complete data was received.                                                 |
+| `null`    | `present` | `present` | Partial data was received alongside field error(s).                         |
+| `present` | `null`    | `null`    | A fetch error happened.                                                     |
+| `present` | `null`    | `present` | 🙅‍♂️ impossible.                                                           |
+| `present` | `present` | `null`    | 🙅‍♂️ impossible.                                                           |
+| `present` | `present` | `present` | 🙅‍♂️ impossible.                                                           |