Don't allow empty include lists

wp1/selection/models/wikiproject.py

@@ -25,6 +25,9 @@ def build(self, content_type, **params):
       raise Wp1FatalSelectionError('Missing param `wp10db`')
     if 'include' not in params:
       raise Wp1FatalSelectionError('Missing param `include`')
+    if not params['include']:
+      raise Wp1FatalSelectionError(
+          'Cannot create selection with empty `include` list')
 
     included_articles = set()
     for project in params['include']:
@@ -42,7 +45,7 @@ def build(self, content_type, **params):
   def validate(self, **params):
     if 'wp10db' not in params:
       raise Wp1FatalSelectionError('Cannot validate without param `wp10db`')
-    if 'include' not in params:
+    if 'include' not in params or not params['include']:
       return ([], [], ['Missing articles to include'])
 
     valid = []

wp1/selection/models/wikiproject_test.py

@@ -63,6 +63,11 @@ def test_validate_missing_include(self):
     actual = self.builder.validate(wp10db=self.wp10db, **params)
     self.assertEqual(([], [], ['Missing articles to include']), actual)
 
+  def test_validate_empty_include(self):
+    params = {'include': [], 'exclude': ['Water Elements', 'Fire']}
+    actual = self.builder.validate(wp10db=self.wp10db, **params)
+    self.assertEqual(([], [], ['Missing articles to include']), actual)
+
   def test_validate_missing_exclude(self):
     params = {'include': ['Water Elements', 'Fire']}
     actual = self.builder.validate(wp10db=self.wp10db, **params)
@@ -142,3 +147,10 @@ def test_build_missing_include(self):
       self.builder.build('text/tab-separated-values',
                          wp10db=self.wp10db,
                          **params)
+
+  def test_build_empty_include(self):
+    params = {'include': [], 'exclude': ['Fire']}
+    with self.assertRaises(Wp1FatalSelectionError):
+      self.builder.build('text/tab-separated-values',
+                         wp10db=self.wp10db,
+                         **params)