Diffing_Engine: Handle nulls

Diffing_Engine/Compute/DiffRevisions.cs

@@ -48,6 +48,18 @@ public static partial class Compute
         [Input("DiffingConfig", "Sets configs such as properties to be ignored in the diffing, or enable/disable property-by-property diffing.")]
         public static Diff DiffRevisions(Revision pastRevision, Revision followingRevision, DiffingConfig diffingConfig = null)
         {
+            if(pastRevision == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot compute the diff between revisions when the past revision is null.");
+                return null;
+            }
+
+            if(followingRevision == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot compute the diff between revisions when the following revision is null.");
+                return null;
+            }
+
             return DiffRevisionObjects(pastRevision.Objects, followingRevision.Objects, diffingConfig);
         }
 

Diffing_Engine/Convert/TryParseObjectToGuid.cs

@@ -45,6 +45,13 @@ public static partial class Convert
 
         public static bool TryParseObjectToGuid(this object obj, out Guid guid)
         {
+            if (obj == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot parse a null object to a GUID.");
+                guid = Guid.Empty;
+                return false;
+            }
+
             guid = Guid.Empty;
 
             // If it's a Guid, extract the Id from there. 

Diffing_Engine/Create/Delta.cs

@@ -48,6 +48,18 @@ public static partial class Create
         [Input("DiffingConfig", "Sets configs such as properties to be ignored in the diffing, or enable/disable property-by-property diffing.\nBy default it takes the DiffingConfig property of the Revision. This input can be used to override it.")]
         public static Delta Delta(Revision pastRevision, Revision currentRevision, DiffingConfig diffingConfig = null, string comment = null)
         {
+            if(pastRevision == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot create a Delta from a null past revision.");
+                return null;
+            }
+
+            if(currentRevision == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot create a Delta from a null current revision.");
+                return null;
+            }
+
             Diff diff = Compute.DiffRevisions(pastRevision, currentRevision, diffingConfig);
 
             return new Delta(pastRevision.StreamId, diff, pastRevision.RevisionId, currentRevision.RevisionId, DateTime.UtcNow.Ticks, m_Author, comment);
@@ -62,6 +74,12 @@ public static Delta Delta(Revision pastRevision, Revision currentRevision, Diffi
         [Input("DiffingConfig", "Sets configs such as properties to be ignored in the diffing, or enable/disable property-by-property diffing.\nBy default it takes the DiffingConfig property of the Revision. This input can be used to override it.")]
         public static Delta Delta(Revision revision, DiffingConfig diffingConfig = null, string comment = null)
         {
+            if(revision == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot create a Delta from a null revision.");
+                return null;
+            }
+
             Diff diff = Compute.DiffRevisions(null, revision, diffingConfig);
 
             return new Delta(revision.StreamId, diff, revision.RevisionId, new Guid(), DateTime.UtcNow.Ticks, m_Author, comment);

Diffing_Engine/Create/Revision.cs

@@ -44,6 +44,18 @@ public static partial class Create
         [Input("diffConfig", "Diffing settings for this Stream Revision. Hashes of objects contained in this stream will be computed based on these configs.")]
         public static Revision Revision(IEnumerable<IBHoMObject> objects, object streamId, string revisionName = null, string comment = null, DiffingConfig diffConfig = null)
         {
+            if(objects == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot create a revision from a null collection of objects.");
+                return null;
+            }
+
+            if(streamId == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot create a revision from a null stream ID.");
+                return null;
+            }
+
             return new Revision(Modify.PrepareForRevision(objects, diffConfig), ProcessStreamId(streamId), diffConfig, revisionName, comment);
         }
 

Diffing_Engine/Query/RevisionFragment.cs

@@ -35,6 +35,12 @@ public static partial class Query
     {
         public static RevisionFragment RevisionFragment(this IBHoMObject obj)
         {
+            if(obj == null)
+            {
+                BH.Engine.Reflection.Compute.RecordError("Cannot query the revision fragment from a null object.");
+                return null;
+            }
+
             return obj.FindFragment<RevisionFragment>(); 
         }
     }