schema property Null safety

1. conduit_open_api
2. open_api_v2
3. APIParameter
4. schema property

APIParameter class

1. Constructors
2. APIParameter
3. Properties
4. allowEmptyValue
5. castMap
6. collectionFormat
7. defaultValue
8. description
9. enumerated
10. exclusiveMaximum
11. exclusiveMinimum
12. extensions
13. format
14. hashCode
15. isRequired
16. items
17. location
18. maximum
19. maxItems
20. maxLength
21. minimum
22. minItems
23. minLength
24. multipleOf
25. name
26. pattern
27. referenceURI
28. representation
29. runtimeType
30. schema
31. type
32. uniqueItems
33. Methods
34. decode
35. encode
36. noSuchMethod
37. toString
38. Operators
39. operator ==