fix behaviour of random values on empty data sets, add tests

random_sets/datasources.py

@@ -122,9 +122,9 @@ class DataSource:
         """
 
         # If there is no data for the specified option, stop now.
-        flattened = [option]
+        flattened = []
         if not self.data[option]:
-            return random.choice(flattened) if rand else flattened
+            raise ValueError(f"There is no data for '{option}' in your data source.")
 
         if hasattr(self.data[option], 'keys'):
             # if the option is a dict, we assume the values are lists; we select a random item

random_sets/sets.py

@@ -22,7 +22,14 @@ class WeightedSet:
             self.members, self.weights = list(zip(*weighted_members))
 
     def random(self) -> str:
-        return random.choices(self.members, self.weights)[0]
+        nonzero_members = []
+        nonzero_weights = []
+        for i in range(self.weights):
+            if float(self.weights[i]) == 0.0:
+                continue
+            nozero_members.append(self.members[i])
+            nozero_weights.append(self.weights[i])
+        return random.choices(nonzero_members, nonzero_weights)[0]
 
     def __add__(self, obj):
         ws = WeightedSet()