fix: serialize empty has-many array

[bf4]

Fixes #174

Root cause:

[].all? # => true
[].any? # => false
[ StoreModel::Model.allocate ].all? { |v| v.is_a?(StoreModel::Model) # => true

So, to check if all are StoreModel::Model, we need to

1. (new) check the array has something in it
2. check that everything in it is a StoreModel::Model

[bf4]

Oddly, even though master is green in Github, I get the same errors locally on master as here.

Failures:

  1) StoreModel::CombineErrorsStrategies::MergeErrorStrategy when parent model has validation keeps parent validation messages
     Failure/Error:
       expect(record.errors.messages).to eq(
         name: ["can't be blank"], configuration: ["Color can't be blank"]
       )

       expected: {:configuration=>["Color can't be blank"], :name=>["can't be blank"]}
            got: #<ActiveModel::DeprecationHandlingMessageHash({:configuration=>#<ActiveModel::DeprecationHandlingMess...or can't be blank"])>, :name=>#<ActiveModel::DeprecationHandlingMessageArray(["can't be blank"])>})>

       (compared using ==)

       Diff:
       @@ -1,3 +1,3 @@
       -:configuration => ["Color can't be blank"],
       -:name => ["can't be blank"],
       +{:name=>["can't be blank"],
       + :configuration=>["is invalid", "Color can't be blank"]}

     # ./spec/store_model/combine_error_strategies/merge_error_strategy_spec.rb:63:in `block (3 levels) in <top (required)>'

  2) StoreModel::Model#parent array store model parent updates parent after assignment
     Failure/Error: expect(configuration.parent).to eq(subject)

       expected: #< configuration: [#<Configuration color: nil, model: nil, active: true, disabled_at: nil, encrypted_serial: nil, type: nil>]>
            got: nil

       (compared using ==)
     Shared Example Group: "for array type" called from ./spec/store_model/model_spec.rb:270
     # ./spec/store_model/model_spec.rb:213:in `block (4 levels) in <top (required)>'

  3) StoreModel::Model#parent json store model parent updates parent after assignment
     Failure/Error: expect(configuration.parent).to eq(subject)

       expected: #< configuration: #<Configuration color: nil, model: nil, active: true, disabled_at: nil, encrypted_serial: nil, type: nil>>
            got: nil

       (compared using ==)
     Shared Example Group: "for singular type" called from ./spec/store_model/model_spec.rb:244
     # ./spec/store_model/model_spec.rb:190:in `block (4 levels) in <top (required)>'

Finished in 0.33743 seconds (files took 0.98431 seconds to load)
342 examples, 3 failures

Failed examples:

rspec ./spec/store_model/combine_error_strategies/merge_error_strategy_spec.rb:49 # StoreModel::CombineErrorsStrategies::MergeErrorStrategy when parent model has validation keeps parent validation messages
rspec ./spec/store_model/model_spec.rb[1:6:2:2:2] # StoreModel::Model#parent array store model parent updates parent after assignment
rspec ./spec/store_model/model_spec.rb[1:6:1:2:2] # StoreModel::Model#parent json store model parent updates parent after assignment

Randomized with seed 16673

[DmitryTsepelev]

LGTM, thank you 🙏