Prevent issues when passing a zero-length list to MeasuredResults.ChangeChromatograms

pwiz_tools/Skyline/FileUI/ManageResultsDlg.cs

@@ -185,19 +185,19 @@ public ManageResultsSettings FormSettings
         {
             get
             {
-                var results = DocumentUIContainer.Document.MeasuredResults ?? MeasuredResults.EMPTY;
+                var chromatograms = DocumentUIContainer.Document.MeasuredResults?.Chromatograms ?? Array.Empty<ChromatogramSet>();
                 var remainingReplicates = listResults.Items.Cast<ManageResultsAction>().Select(a => a.Chromatograms);
 
                 // only keep renames where there's still a replicate with the new name
                 var renamed = _renamedReplicates.Where(r => remainingReplicates.Any(rep => rep.Name == r.Value))
                     .Select(r => new RenamedReplicate(r.Key, r.Value)).ToList();
 
-                var removed = results.Chromatograms.Except(remainingReplicates)
+                var removed = chromatograms.Except(remainingReplicates)
                     .Where(chrom => renamed.All(r => r.OldName != chrom.Name))
                     .Select(c => c.Name).ToList();
 
                 return new ManageResultsSettings(renamed, removed,
-                    LibraryRunsRemovedList, removed.Count == results.Chromatograms.Count,
+                    LibraryRunsRemovedList, removed.Count == chromatograms.Count,
                     IsRemoveAllLibraryRuns,
                     IsRemoveCorrespondingReplicates, IsRemoveCorrespondingLibraries);
             }

pwiz_tools/Skyline/Model/DocSettings/SrmSettings.cs

@@ -531,9 +531,17 @@ public SrmSettings ChangeDataSettings(DataSettings prop)
 
         public SrmSettings ChangeMeasuredResults(MeasuredResults prop)
         {
+            ValidateMeasuredResults(prop);
+
             return ChangeProp(ImClone(this), im => im.MeasuredResults = prop);
         }
 
+        private void ValidateMeasuredResults(MeasuredResults measuredResults)
+        {
+            if (measuredResults != null && measuredResults.Chromatograms.Count == 0)
+                throw new ArgumentException(@"MeasuredResults must have at least one ChromatogramSet. Use null to remove all results.");
+        }
+
         public SrmSettings ChangeIsResultsJoiningDisabled(bool prop)
         {
             return ChangeProp(ImClone(this), im =>
@@ -2282,13 +2290,13 @@ public override void ReadXml(XmlReader reader)
             // We want Skyline to be able to read older documents where <measured_results> come before <data_settings>
             if (reader.IsStartElement(new XmlElementHelper<MeasuredResults>().ElementNames[0]))
             {
-                MeasuredResults = reader.DeserializeElement<MeasuredResults>();
+                MeasuredResults = reader.DeserializeElement<MeasuredResults>()?.NullIfEmpty();
                 DataSettings = reader.DeserializeElement<DataSettings>() ?? DataSettings.DEFAULT;   
             }
             else
             {
                 DataSettings = reader.DeserializeElement<DataSettings>() ?? DataSettings.DEFAULT;
-                MeasuredResults = reader.DeserializeElement<MeasuredResults>();
+                MeasuredResults = reader.DeserializeElement<MeasuredResults>()?.NullIfEmpty();
             }
             DocumentRetentionTimes = reader.DeserializeElement<DocumentRetentionTimes>() ?? DocumentRetentionTimes.EMPTY;
             reader.ReadEndElement();

pwiz_tools/Skyline/Model/Results/MeasuredResults.cs

@@ -35,8 +35,6 @@ namespace pwiz.Skyline.Model.Results
     [XmlRoot("measured_results")]
     public sealed class MeasuredResults : Immutable, IXmlSerializable
     {
-        public static readonly MeasuredResults EMPTY = new MeasuredResults(new ChromatogramSet[0]);
-
         private static readonly HashSet<MsDataFileUri> EMPTY_FILES = new HashSet<MsDataFileUri>();
 
         private ImmutableList<ChromatogramSet> _chromatograms;
@@ -64,9 +62,14 @@ public MeasuredResults(IList<ChromatogramSet> chromatograms, bool disableJoining
             IsTimeNormalArea = true;
         }
 
-        public bool IsEmpty
+        /// <summary>
+        /// Returns null if Chromatograms is empty to help with assignment
+        /// to SrmSettings, which does not allow MeasuredResults with empty
+        /// Chromatograms, but requires null instead in this case.
+        /// </summary>
+        public MeasuredResults NullIfEmpty()
         {
-            get { return _chromatograms == null || _chromatograms.Count == 0; }
+            return Chromatograms.Count == 0 ? null : this;
         }
 
         [TrackChildren]