clearContext method Null safety

1. spine_client
2. subscription.pb
3. Topic
4. clearContext method

Topic class

1. Constructors
2. Topic
3. fromBuffer
4. fromJson
5. Properties
6. context
7. eventPlugin
8. fieldMask
9. hashCode
10. id
11. info_
12. isFrozen
13. runtimeType
14. target
15. unknownFields
16. Methods
17. $_ensure
18. $_get
19. $_getB
20. $_getBF
21. $_getI
22. $_getI64
23. $_getIZ
24. $_getList
25. $_getMap
26. $_getN
27. $_getS
28. $_getSZ
29. $_has
30. $_setBool
31. $_setBytes
32. $_setDouble
33. $_setFloat
34. $_setInt64
35. $_setSignedInt32
36. $_setString
37. $_setUnsignedInt32
38. $_whichOneof
39. addExtension
40. check
41. clear
42. clearContext
43. clearExtension
44. clearField
45. clearFieldMask
46. clearId
47. clearTarget
48. clone
49. copyWith
50. createEmptyInstance
51. createMapField
52. createRepeatedField
53. ensureContext
54. ensureFieldMask
55. ensureId
56. ensureTarget
57. extensionsAreInitialized
58. freeze
59. getDefaultForField
60. getExtension
61. getField
62. getFieldOrNull
63. getTagNumber
64. hasContext
65. hasExtension
66. hasField
67. hasFieldMask
68. hasId
69. hasRequiredFields
70. hasTarget
71. isInitialized
72. mergeFromBuffer
73. mergeFromCodedBufferReader
74. mergeFromJson
75. mergeFromJsonMap
76. mergeFromMessage
77. mergeFromProto3Json
78. mergeUnknownFields
79. noSuchMethod
80. setExtension
81. setField
82. toBuilder
83. toDebugString
84. toProto3Json
85. toString
86. writeToBuffer
87. writeToCodedBufferWriter
88. writeToJson
89. writeToJsonMap
90. Operators
91. operator ==
92. Static methods
93. create
94. createRepeated
95. getDefault