fix code to avoid flutter analyze errors

[TP-113]

Some parts in the current code are causing errors in the flutter analyzer, and the errors are also displayed in the IDE.
I fix the code to avoid errors.

↓flutter analyze result

before

info • To-do comment doesn't follow the Flutter style • lib/firebase_database_mocks.dart:1:1 • flutter_style_todos
   info • To-do comment doesn't follow the Flutter style • lib/firebase_database_mocks.dart:2:1 • flutter_style_todos
   info • Local variables should be final • lib/src/mock_data_snapshot.dart:28:7 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_data_snapshot.dart:42:7 • prefer_final_locals
  error • The argument type 'dynamic' can't be assigned to the parameter type 'String'.  • lib/src/mock_data_snapshot.dart:56:57 • argument_type_not_assignable
warning • The type of nodePath can't be inferred; a type must be explicitly provided • lib/src/mock_database_reference.dart:18:27 • inference_failure_on_untyped_parameter
  error • The argument type 'dynamic' can't be assigned to the parameter type 'String'.  • lib/src/mock_database_reference.dart:19:18 • argument_type_not_assignable
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:22:3 • flutter_style_todos
   info • The member 'onValue' overrides an inherited member but isn't annotated with '@override' • lib/src/mock_database_reference.dart:23:29 • annotate_overrides
  error • Conditions must have a static type of 'bool' • lib/src/mock_database_reference.dart:28:9 • non_bool_condition
warning • The type of data can't be inferred; a type must be explicitly provided • lib/src/mock_database_reference.dart:34:13 • inference_failure_on_untyped_parameter
  error • Conditions must have a static type of 'bool' • lib/src/mock_database_reference.dart:35:9 • non_bool_condition
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, dynamic>?' • lib/src/mock_database_reference.dart:36:24 • invalid_assignment
   info • Assignment to a variable of type 'void' • lib/src/mock_database_reference.dart:38:7 • void_checks
   info • Statements in an if should be enclosed in a block • lib/src/mock_database_reference.dart:38:7 • curly_braces_in_flow_control_structures
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, dynamic>?' • lib/src/mock_database_reference.dart:38:30 • invalid_assignment
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:78:5 • flutter_style_todos
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, Object?>' • lib/src/mock_database_reference.dart:90:13 • invalid_assignment
   info • The local variable '_baseData' starts with an underscore • lib/src/mock_database_reference.dart:91:26 • no_leading_underscores_for_local_identifiers
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, dynamic>' • lib/src/mock_database_reference.dart:98:19 • invalid_assignment
   info • The local variable '_key' starts with an underscore • lib/src/mock_database_reference.dart:101:14 • no_leading_underscores_for_local_identifiers
   info • The variable '_key' should be final • lib/src/mock_database_reference.dart:101:14 • prefer_final_in_for_each
   info • The local variable '_data' starts with an underscore • lib/src/mock_database_reference.dart:104:13 • no_leading_underscores_for_local_identifiers
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:114:7 • flutter_style_todos
   info • The local variable '_data' starts with an underscore • lib/src/mock_database_reference.dart:155:27 • no_leading_underscores_for_local_identifiers
   info • The variable 'segment' should be final • lib/src/mock_database_reference.dart:156:14 • prefer_final_in_for_each
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, dynamic>?' • lib/src/mock_database_reference.dart:169:15 • invalid_assignment
   info • Local variables should be final • lib/src/mock_database_reference.dart:182:5 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_database_reference.dart:186:9 • prefer_final_locals
  error • A value of type 'dynamic' can't be assigned to a variable of type 'Map<String, dynamic>?' • lib/src/mock_database_reference.dart:191:22 • invalid_assignment
   info • Local variables should be final • lib/src/mock_database_reference.dart:204:5 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_database_reference.dart:210:5 • prefer_final_locals
warning • The return type of 'persistData' cannot be inferred • lib/src/mock_firebase_database.dart:9:14 • inference_failure_on_function_return_type
   info • The private field _volatileData could be 'final' • lib/src/mock_firebase_database.dart:11:24 • prefer_final_fields
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_firebase_database.dart:24:3 • flutter_style_todos
   info • The method is used to change a property • lib/src/mock_firebase_database.dart:25:15 • use_setters_to_change_properties
   info • The local variable '_lastPushTime' starts with an underscore • lib/src/util.dart:13:7 • no_leading_underscores_for_local_identifiers
   info • The local variable '_lastRandChars' starts with an underscore • lib/src/util.dart:16:9 • no_leading_underscores_for_local_identifiers
   info • The local variable '_random' starts with an underscore • lib/src/util.dart:17:9 • no_leading_underscores_for_local_identifiers
   info • Local variables should be final • test/mock_data_snapshot_test.dart:41:7 • prefer_final_locals
   info • Local variables should be final • test/mock_data_snapshot_test.dart:57:7 • prefer_final_locals
   info • Unnecessary use of parentheses • test/mock_data_snapshot_test.dart:65:26 • unnecessary_parenthesis
   info • Unnecessary use of parentheses • test/mock_data_snapshot_test.dart:70:22 • unnecessary_parenthesis
warning • The type argument(s) of 'List' can't be inferred • test/mock_data_snapshot_test.dart:72:37 • inference_failure_on_collection_literal
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:113:7 • flutter_style_todos
   info • The value of the argument is redundant because it matches the default value • test/mock_database_reference_test.dart:212:63 • avoid_redundant_argument_values
   info • The value of the argument is redundant because it matches the default value • test/mock_database_reference_test.dart:216:63 • avoid_redundant_argument_values
   info • The local variable '_databaseReference' starts with an underscore • test/mock_database_reference_test.dart:217:30 • no_leading_underscores_for_local_identifiers
   info • Local variables should be final • test/mock_database_reference_test.dart:224:7 • prefer_final_locals
   info • Don't invoke 'print' in production code • test/mock_database_reference_test.dart:229:7 • avoid_print
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:465:5 • flutter_style_todos
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:474:3 • flutter_style_todos

after

  info • To-do comment doesn't follow the Flutter style • lib/firebase_database_mocks.dart:1:1 • flutter_style_todos
   info • To-do comment doesn't follow the Flutter style • lib/firebase_database_mocks.dart:2:1 • flutter_style_todos
   info • Local variables should be final • lib/src/mock_data_snapshot.dart:28:7 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_data_snapshot.dart:42:7 • prefer_final_locals
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:22:3 • flutter_style_todos
   info • The member 'onValue' overrides an inherited member but isn't annotated with '@override' • lib/src/mock_database_reference.dart:23:29 • annotate_overrides
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:79:5 • flutter_style_todos
   info • The local variable '_baseData' starts with an underscore • lib/src/mock_database_reference.dart:92:26 • no_leading_underscores_for_local_identifiers
   info • The local variable '_key' starts with an underscore • lib/src/mock_database_reference.dart:102:14 • no_leading_underscores_for_local_identifiers
   info • The variable '_key' should be final • lib/src/mock_database_reference.dart:102:14 • prefer_final_in_for_each
   info • The local variable '_data' starts with an underscore • lib/src/mock_database_reference.dart:105:13 • no_leading_underscores_for_local_identifiers
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_database_reference.dart:115:7 • flutter_style_todos
   info • The local variable '_data' starts with an underscore • lib/src/mock_database_reference.dart:156:27 • no_leading_underscores_for_local_identifiers
   info • The variable 'segment' should be final • lib/src/mock_database_reference.dart:157:14 • prefer_final_in_for_each
   info • Local variables should be final • lib/src/mock_database_reference.dart:183:5 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_database_reference.dart:187:9 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_database_reference.dart:205:5 • prefer_final_locals
   info • Local variables should be final • lib/src/mock_database_reference.dart:211:5 • prefer_final_locals
   info • The private field _volatileData could be 'final' • lib/src/mock_firebase_database.dart:11:24 • prefer_final_fields
   info • To-do comment doesn't follow the Flutter style • lib/src/mock_firebase_database.dart:24:3 • flutter_style_todos
   info • The method is used to change a property • lib/src/mock_firebase_database.dart:25:15 • use_setters_to_change_properties
   info • The local variable '_lastPushTime' starts with an underscore • lib/src/util.dart:13:7 • no_leading_underscores_for_local_identifiers
   info • The local variable '_lastRandChars' starts with an underscore • lib/src/util.dart:16:9 • no_leading_underscores_for_local_identifiers
   info • The local variable '_random' starts with an underscore • lib/src/util.dart:17:9 • no_leading_underscores_for_local_identifiers
   info • Local variables should be final • test/mock_data_snapshot_test.dart:41:7 • prefer_final_locals
   info • Local variables should be final • test/mock_data_snapshot_test.dart:57:7 • prefer_final_locals
   info • Unnecessary use of parentheses • test/mock_data_snapshot_test.dart:65:26 • unnecessary_parenthesis
   info • Unnecessary use of parentheses • test/mock_data_snapshot_test.dart:70:22 • unnecessary_parenthesis
warning • The type argument(s) of 'List' can't be inferred • test/mock_data_snapshot_test.dart:72:37 • inference_failure_on_collection_literal
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:113:7 • flutter_style_todos
   info • The value of the argument is redundant because it matches the default value • test/mock_database_reference_test.dart:212:63 • avoid_redundant_argument_values
   info • The value of the argument is redundant because it matches the default value • test/mock_database_reference_test.dart:216:63 • avoid_redundant_argument_values
   info • The local variable '_databaseReference' starts with an underscore • test/mock_database_reference_test.dart:217:30 • no_leading_underscores_for_local_identifiers
   info • Local variables should be final • test/mock_database_reference_test.dart:224:7 • prefer_final_locals
   info • Don't invoke 'print' in production code • test/mock_database_reference_test.dart:229:7 • avoid_print
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:465:5 • flutter_style_todos
   info • To-do comment doesn't follow the Flutter style • test/mock_database_reference_test.dart:474:3 • flutter_style_todos

[sitatec]

LGTM, Thanks 👍🏾