diff --git a/rest_framework/utils/serializer_helpers.py b/rest_framework/utils/serializer_helpers.py
index 415e291c9..b2e0fc80e 100644
--- a/rest_framework/utils/serializer_helpers.py
+++ b/rest_framework/utils/serializer_helpers.py
@@ -101,6 +101,9 @@ class NestedBoundField(BoundField):
         return BoundField(field, value, error, prefix=self.name + '.')
 
     def as_form_field(self):
+        if self.value is None:
+            return ''
+
         values = {}
         for key, value in self.value.items():
             if isinstance(value, (list, dict)):