Unable to add component in Sitecore SXA using Experience Editor

Question

I have just installed the vanilla Sitecore 9.1.1 and SXA 1.8 on the local machine.

1. Created the demo website.
2. Upon adding any component in experience editor it throws below error.

Error:

9188 09:38:41 ERROR Application error.
Exception: System.Web.HttpUnhandledException
Message: Exception of type 'System.Web.HttpUnhandledException' was thrown.
Source: System.Web
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Nested Exception

Exception: System.NullReferenceException
Message: Object reference not set to an instance of an object.
Source: Sitecore.XA.Feature.Composites
   at Sitecore.XA.Feature.Composites.Pipelines.ExecutePageEditorAction.FillCompositeRenderingDatasource.Process(PipelineArgs args)
   at (Object , Object )
   at Sitecore.Pipelines.CorePipeline.Run(PipelineArgs args)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain, Boolean failIfNotExists)
   at Sitecore.Pipelines.DefaultCorePipelineManager.Run(String pipelineName, PipelineArgs args, String pipelineDomain)
   at Sitecore.Pipelines.ExecutePageEditorAction.ExecutePageEditorActionPipeline.Run(ExecutePageEditorActionArgs args)
   at Sitecore.Shell.Applications.WebEdit.Palette.OnPreInit(EventArgs e)
   at System.Web.UI.Page.PerformPreInit()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Answer 1

It turned out that \App_Config\Modules\SXA\Feature\Sitecore.XA.Feature.Composites.config was disabled, due to which services specified in the file were not registered and resulted in the null exception.