Fixed: sqlalchemy#1369 get_x_arguments(as_dictionary=True) for args…

… without `=`

alembic/context.pyi

@@ -759,7 +759,8 @@ def get_x_argument(
     The return value is a list, returned directly from the ``argparse``
     structure.  If ``as_dictionary=True`` is passed, the ``x`` arguments
     are parsed using ``key=value`` format into a dictionary that is
-    then returned.
+    then returned. If there is no `=` in the argument, value is an empty
+    string.
 
     For example, to support passing a database URL on the command line,
     the standard ``env.py`` script can be modified like this::

alembic/runtime/environment.py

@@ -367,7 +367,8 @@ def get_x_argument(
         The return value is a list, returned directly from the ``argparse``
         structure.  If ``as_dictionary=True`` is passed, the ``x`` arguments
         are parsed using ``key=value`` format into a dictionary that is
-        then returned.
+        then returned. If there is no `=` in the argument, value is an empty
+        string.
 
         For example, to support passing a database URL on the command line,
         the standard ``env.py`` script can be modified like this::
@@ -401,7 +402,15 @@ def get_x_argument(
         else:
             value = []
         if as_dictionary:
-            value = dict(arg.split("=", 1) for arg in value)
+            dict_value = {}
+            for arg in value:
+                try:
+                    x_key, x_value = arg.split("=", 1)
+                except ValueError:
+                    x_key, x_value = arg, ""
+                dict_value[x_key] = x_value
+            value = dict_value
+
         return value
 
     def configure(

tests/test_environment.py

@@ -54,6 +54,11 @@ def test_x_arg_no_opts_asdict(self):
         env = self._fixture()
         eq_(env.get_x_argument(as_dictionary=True), {})
 
+    def test_x_arg_empty_value(self):
+        env = self._fixture()
+        self.cfg.cmd_opts = mock.Mock(x=["y"])
+        eq_(env.get_x_argument(as_dictionary=True), {"y": ""})
+
     def test_tag_arg(self):
         env = self._fixture(tag="x")
         eq_(env.get_tag_argument(), "x")