Null boolean parameter is coerced to false when Java type is primitive boolean

```graphql
mutation  {
  createCat(enabled: Boolean): Cat! 
}
```

```java
public Cat createCat(boolean enabled) {
   ...
}
```

when executing: 
```graphql
mutation {
  createCat {
    id
   }
}
```

The value of `enabled` gets coerced to `false`. Instead, this should throw and require a nullable `Boolean` type to be used instead. Preferably it should throw at startup.