Fix null ref when ExtractionInformation deleted

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Row size no longer cuts off bottom pixels of column name(s)
   - Multi delete is now supported
   - Pasted column name(s) with spaces e.g. `[my cool col]` now work
+- Fixed null reference in extraction checks when extracting a dataset where the original [ExtractionInformation] has been deleted [#1253](https://github.com/HicServices/RDMP/issues/1253)
 
 ## [7.0.14] - 2022-06-27
 

Rdmp.Core/DataExport/Checks/SelectedDataSetsChecker.cs

@@ -88,6 +88,20 @@ public void Check(ICheckNotifier notifier)
                 .Select(c => c.CatalogueExtractionInformation)
                 .ToArray();
 
+            var orphans = selectedcols
+                .OfType<ExtractableColumn>()
+                .Where(c => c.CatalogueExtractionInformation == null)
+                .ToArray();
+
+            if(orphans.Any())
+            {
+                notifier.OnCheckPerformed(
+                    new CheckEventArgs("The following columns no longer map to an ExtractionInformation (it may have been deleted)" + Environment.NewLine
+                    + string.Join(Environment.NewLine, orphans.Select(o => o.GetRuntimeName()).ToArray()),
+                    CheckResult.Warning));
+            }
+
+
             WarnAboutExtractionCategory(notifier, config, ds,eis, ErrorCodes.ExtractionContainsSpecialApprovalRequired, ExtractionCategory.SpecialApprovalRequired);
             WarnAboutExtractionCategory(notifier, config, ds, eis, ErrorCodes.ExtractionContainsInternal, ExtractionCategory.Internal);
             WarnAboutExtractionCategory(notifier, config, ds, eis, ErrorCodes.ExtractionContainsDeprecated, ExtractionCategory.Deprecated);
@@ -284,7 +298,7 @@ private bool IsTextDatatype(IColumn arg)
         /// <param name="category"></param>
         public static void WarnAboutExtractionCategory(ICheckNotifier notifier, IExtractionConfiguration configuration, IExtractableDataSet dataset, ExtractionInformation[] cols, ErrorCode errorCode, ExtractionCategory category)
         {
-            if (cols.Any(c => c.ExtractionCategory == category))
+            if (cols.Any(c => c?.ExtractionCategory == category))
             {
                 notifier.OnCheckPerformed(new CheckEventArgs(errorCode, configuration, dataset,
                     String.Join(",", cols.Where(c => c.ExtractionCategory == category)