Improve annotation handling and date retrieval robustness

Refactored annotation processing in PDFBurner.vb to handle null elements and annotations safely, preventing possible errors and improving code clarity. Updated GetSignedDate in ReceiverModel.vb to ensure consistent DateTime return values, handle DBNull and type conversions, and improve error handling.

EnvelopeGenerator.CommonServices/Models/ReceiverModel.vb

@@ -270,12 +270,26 @@ Public Class ReceiverModel
     Private Function GetSignedDate(pEmailAddress As String, pEnvelopeId As Integer) As Date
         Try
             Dim oStatusInt As Integer = EnvelopeStatus.DocumentSigned
-            Return Database.GetScalarValue($"SELECT ACTION_DATE FROM [DD_ECM].[dbo].[TBSIG_ENVELOPE_HISTORY] WHERE ENVELOPE_ID = {pEnvelopeId}
+            Dim value = Database.GetScalarValue($"SELECT ACTION_DATE FROM [DD_ECM].[dbo].[TBSIG_ENVELOPE_HISTORY] WHERE ENVELOPE_ID = {pEnvelopeId}
                                                 And USER_REFERENCE = '{pEmailAddress}' AND [STATUS] = {oStatusInt}")
 
+            If value Is Nothing OrElse value Is DBNull.Value Then
+                Return DateTime.MinValue
+            End If
+
+            If TypeOf value Is DateTime Then
+                Return DirectCast(value, DateTime)
+            End If
+
+            Dim parsedDate As DateTime
+            If DateTime.TryParse(value.ToString(), parsedDate) Then
+                Return parsedDate
+            End If
+
+            Return DateTime.MinValue
         Catch ex As Exception
             Logger.Error(ex)
-            Return Nothing
+            Return DateTime.MinValue
         End Try
     End Function