common/extensions/null_extension library

1. json_component package
2. documentation
3. common/extensions/null_extension.dart

json_component package

1. Libraries
2. common/extensions/null_extension
3. common/extensions/string_extension
4. common/types/component_exception
5. common/types/component_type
6. component_builder
7. components/base_json_component
8. json_component