Strings: handle null values from the API as empty strings to match the current behavior with arrays.

Author: PMeira

dss/_cffi_api_util.py

@@ -146,7 +146,9 @@ def clear_buffers(self):
         self.init_buffers()
 
     def get_string(self, b):
-        return self.ffi.string(b).decode(self.codec)
+        if b != self.ffi.NULL:
+            return self.ffi.string(b).decode(self.codec)
+        return ''
 
     def get_float64_array(self, func, *args):
         ptr = self.ffi.new('double**')