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/Jobs/FinalizeDocument/PDFBurner.vb

@@ -85,16 +85,37 @@ Namespace Jobs.FinalizeDocument
 
                     'Add annotations
                     For Each element In elements
+                        If element Is Nothing Then
+                            Continue For
+                        End If
+
+                        Dim elementAnnotations = If(element.Annotations, Enumerable.Empty(Of ElementAnnotation)())
+                        If Not elementAnnotations.Any() Then
+                            Continue For
+                        End If
 
                         Dim frameX = (element.Left - 0.7 - margin)
 
-                        Dim frame = element.Annotations.FirstOrDefault(Function(a) a.Name = "frame")
+                        Dim frame = elementAnnotations.FirstOrDefault(Function(a) a.Name = "frame")
                         Dim frameY = element.Top - 0.5 - margin
-                        Dim frameYShift = frame.Y - frameY * inchFactor
-                        Dim frameXShift = frame.X - frameX * inchFactor
+                        Dim frameYShift As Double = 0
+                        Dim frameXShift As Double = 0
+
+                        If frame IsNot Nothing Then
+                            frameYShift = frame.Y - frameY * inchFactor
+                            frameXShift = frame.X - frameX * inchFactor
+                        End If
+
+                        For Each annot In elementAnnotations
+                            If annot Is Nothing Then
+                                Continue For
+                            End If
+
+                            Dim yOffsetofFF As Double = 0
+                            If Not String.IsNullOrEmpty(annot.Name) Then
+                                yOffsetsOfFF.TryGetValue(annot.Name, yOffsetofFF)
+                            End If
 
-                        For Each annot In element.Annotations
-                            Dim yOffsetofFF As Double = If(yOffsetsOfFF.TryGetValue(annot.Name, yOffsetofFF), yOffsetofFF, 0)
                             Dim y = frameY + yOffsetofFF
 
                             If annot.Type = AnnotationType.FormField Then