Make sure posterior save delta function

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 Changes currently on master, but not under a tag.
 
+### Changes
+- Make filling in posterior with fixed parameters work
+
 ## [0.3] 2018-01-02
 
 ### Added

bilby/core/result.py

@@ -549,12 +549,14 @@ class Result(dict):
         if hasattr(self, 'posterior') is False:
             data_frame = pd.DataFrame(
                 self.samples, columns=self.search_parameter_keys)
-            data_frame['log_likelihood'] = getattr(
-                self, 'log_likelihood_evaluations', np.nan)
             for key in priors:
-                if getattr(priors[key], 'is_fixed', False):
+                if isinstance(priors[key], DeltaFunction):
                     data_frame[key] = priors[key].peak
-            # We save the samples in the posterior and remove the array of samples
+                elif isinstance(priors[key], float):
+                    data_frame[key] = priors[key]
+            data_frame['log_likelihood'] = getattr(
+                self, 'log_likelihood_evaluations', np.nan)
+            # remove the array of samples
             del self.samples
         else:
             data_frame = self.posterior