Sitecore 10 - Issue during the serialization (SCS) push - GraphQL.Common.Response.GraphQLResponse

 Recently, I got the below error while working on Sitecore 10 with content serialization.

Unhandled exception: System.Exception: Unhandled exception

 ---> System.AggregateException: One or more errors occurred. (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.) (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.) (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.) (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.) (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.) (Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.)

 ---> Newtonsoft.Json.JsonSerializationException: Error converting value 404 to type 'GraphQL.Common.Response.GraphQLResponse'. Path '', line 1, position 3.

 ---> System.ArgumentException: Could not cast or convert from System.Int64 to GraphQL.Common.Response.GraphQLResponse.

   at Newtonsoft.Json.Utilities.ConvertUtils.EnsureTypeAssignable(Object value, Type initialType, Type targetType)

   at Newtonsoft.Json.Utilities.ConvertUtils.ConvertOrCast(Object initialValue, CultureInfo culture, Type targetType)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)

   --- End of inner exception stack trace ---

   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)

   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)

   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)

   at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)

   at GraphQL.Client.Http.Internal.GraphQLHttpHandler.ReadHttpResponseMessageAsync(HttpResponseMessage httpResponseMessage)

   at GraphQL.Client.Http.Internal.GraphQLHttpHandler.PostAsync(GraphQLRequest request, CancellationToken cancellationToken)

   at Sitecore.DevEx.Serialization.Client.Datasources.Sc.SitecoreApiClient.<>c__DisplayClass13_0.<<RunQuery>b__0>d.MoveNext() in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Serialization.Client\Datasources\Sc\SitecoreApiClient.cs:line 127

--- End of stack trace from previous location where exception was thrown ---

   at Sitecore.DevEx.Configuration.Authentication.OidcAuthenticationProvider.MakeAuthenticatedRequestInternal(HttpClient client, Func`2 requestAction) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Configuration\Authentication\OidcAuthenticationProvider.cs:line 80

   at Sitecore.DevEx.Configuration.Authentication.OidcAuthenticationProvider.MakeAuthenticatedRequest(HttpClient client, Func`2 requestAction) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Configuration\Authentication\OidcAuthenticationProvider.cs:line 25

   at Sitecore.DevEx.Configuration.Authentication.ClientCredentialsAuthenticationProvider.MakeAuthenticatedRequest(HttpClient client, Func`2 requestAction) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Configuration\Authentication\ClientCredentialsAuthenticationProvider.cs:line 90

   at Sitecore.DevEx.Configuration.Models.EnvironmentConfiguration.MakeAuthenticatedRequest(HttpClient client, Func`2 requestAction) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Configuration\Models\EnvironmentConfiguration.cs:line 168

   at Sitecore.DevEx.Serialization.Client.Datasources.Sc.SitecoreApiClient.RunQuery(String servicePath, GraphQLRequest request, Boolean assertNoErrors, CancellationToken cancellationToken) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Serialization.Client\Datasources\Sc\SitecoreApiClient.cs:line 155

   at Sitecore.DevEx.Serialization.Client.Datasources.Sc.Query.SitecoreTreeDataStore.ExecuteSingleBatchQuery[T](String batchQueryFragment, TreeScope scope, ItemSpec[] specs, CancellationToken cancellationToken) in C:\BA\4c1e764e9356dfd1\src\Sitecore.DevEx.Serialization.Client\Datasources\Sc\Query\SitecoreTreeDataStore.cs:line 402

Investigation - I did the git clean up and I think the cleanup has removed a few files or so

Steps -  I build the solution and it was working fine,  I ran the SerPush command again and now this time got the error that one of the scripts is missing from the Theme Component

did not exist in serialized items (66 subtrees) data store. An empty source indicates that you need to fill that source with data before attempting to push it into a destination. Usually, that means you need to pull an initial data set from Sitecore to fill serialized files before being able to push serialized data into Sitecore.

I restored the missing file and the issue got resolved.