Improve Error handling across the board

MultiTool.Common/Documents/Document.vb

@@ -26,6 +26,8 @@ Namespace Documents
         ''' </summary>
         Public Property Selected As Boolean = False
 
+        Private DocumentErrors As New List(Of DocumentError)
+
         Public ReadOnly Property HasErrors As Boolean
             Get
                 Return Errors.Count > 0
@@ -34,8 +36,11 @@ Namespace Documents
 
         Public ReadOnly Property Errors As List(Of String)
             Get
-                Dim oRowErrors = Rows.SelectMany(Function(row) row.Errors).ToList()
-                Dim oDocumentErrors As List(Of String) = GetDocumentErrors().
+                Dim oRowErrors = Rows.
+                    SelectMany(Function(row) row.Errors, Function(row, err) err.ToString).
+                    ToList()
+
+                Dim oDocumentErrors As List(Of String) = DocumentErrors.
                     Select(Function(err) err.ToString()).
                     ToList()
                 Return oDocumentErrors.
@@ -44,6 +49,13 @@ Namespace Documents
             End Get
         End Property
 
+        Public Sub AddDocumentError(pDocumentError As DocumentErrorType, pMessage As String)
+            DocumentErrors.Add(New DocumentError With {
+                .Type = pDocumentError,
+                .Message = pMessage
+            })
+        End Sub
+
         Public ReadOnly Property MandatorId As String
             Get
                 Return Mandator?.Id
@@ -84,19 +96,12 @@ Namespace Documents
         End Function
 
         Public Overrides Function Equals(obj As Object) As Boolean
-            Return FullName = DirectCast(obj, Document).FullName
-        End Function
-
-        Private Function GetDocumentErrors() As List(Of DocumentError)
-            Dim oErrors As New List(Of DocumentError)
-
-            If Mandator Is Nothing Then
-                oErrors.Add(DocumentError.MandatorNotFound)
+            If obj Is Nothing Then
+                Return False
             End If
 
-            Return oErrors
+            Return FullName = DirectCast(obj, Document).FullName
         End Function
-
     End Class
 
 End Namespace