diff --git a/nifty/field.py b/nifty/field.py
index eddc59009fbc95d5ac2ef61bfc01131b029a5bab..5796f78bc6540db2564ae523a26fc06d3cd877de 100644
--- a/nifty/field.py
+++ b/nifty/field.py
@@ -90,9 +90,11 @@ class Field(Loggable, Versionable, object):
             try:
                 dtype = val.dtype
             except AttributeError:
-                if val is not None:
+                try:
+                    if val is None:
+                        raise TypeError
                     dtype = np.result_type(val)
-        else:
+                except(TypeError):
                     dtype = np.dtype(gc['default_field_dtype'])
         else:
             dtype = np.dtype(dtype)
@@ -307,6 +309,9 @@ class Field(Loggable, Versionable, object):
         # check if the `spaces` input is valid
         spaces = utilities.cast_axis_to_tuple(spaces, len(self.domain))
 
+        if spaces is None:
+            spaces = range(len(self.domain))
+
         for power_space_index in spaces:
             power_space = self.domain[power_space_index]
             if not isinstance(power_space, PowerSpace):