diff --git a/shapefile.py b/shapefile.py
index f57ef31..2011172 100644
--- a/shapefile.py
+++ b/shapefile.py
@@ -482,7 +482,7 @@ def __record(self):
                 continue
             elif typ == "N":
                 value = value.replace(b('\0'), b('')).strip()
-                if value == b(''):
+                if value == b('') or value == b('**'):
                     value = 0
                 elif deci:
                     value = float(value)
@@ -646,7 +646,8 @@ def __bbox(self, shapes, shapeTypes=[]):
             shapeType = self.shapeType
             if shapeTypes:
                 shapeType = shapeTypes[shapes.index(s)]
-            px, py = list(zip(*s.points))[:2]
+            if len(s.points):
+                px, py = list(zip(*s.points))[:2]
             x.extend(px)
             y.extend(py)
         return [min(x), min(y), max(x), max(y)]
@@ -821,7 +822,8 @@ def __shpRecords(self):
             # Write a single point
             if s.shapeType in (1,11,21):
                 try:
-                    f.write(pack("<2d", s.points[0][0], s.points[0][1]))
+                    if len(s.points) and len(s.points[0])>1:
+                        f.write(pack("<2d", s.points[0][0], s.points[0][1]))
                 except error:
                     raise ShapefileException("Failed to write point for record %s. Expected floats." % recNum)
             # Write a single Z value