From 28d37a9c57e0fcdfbe129e763e8a7f1d108ed9ee Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Fri, 21 Aug 2015 11:59:52 -0400
Subject: [PATCH] - Repaired the render operation for the
 :class:`.ops.AlterColumnOp` object to succeed when the "existing_type" field
 was not present.

---
 alembic/autogenerate/render.py |  7 ++++---
 docs/build/changelog.rst       |  6 ++++++
 tests/test_autogen_render.py   | 10 ++++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/alembic/autogenerate/render.py b/alembic/autogenerate/render.py
index 182f5de9..e7a616ef 100644
--- a/alembic/autogenerate/render.py
+++ b/alembic/autogenerate/render.py
@@ -349,9 +349,10 @@ def _alter_column(autogen_context, op):
             autogen_context),
         'tname': tname,
         'cname': cname}
-    text += ",\n%sexisting_type=%s" % (
-        indent,
-        _repr_type(existing_type, autogen_context))
+    if existing_type is not None:
+        text += ",\n%sexisting_type=%s" % (
+            indent,
+            _repr_type(existing_type, autogen_context))
     if server_default is not False:
         rendered = _render_server_default(
             server_default, autogen_context)
diff --git a/docs/build/changelog.rst b/docs/build/changelog.rst
index e0f8b7f2..b1d72efc 100644
--- a/docs/build/changelog.rst
+++ b/docs/build/changelog.rst
@@ -6,6 +6,12 @@ Changelog
 .. changelog::
     :version: 0.8.1
 
+    .. change::
+      :tags: bug, autogenerate
+
+      Repaired the render operation for the :class:`.ops.AlterColumnOp` object
+      to succeed when the "existing_type" field was not present.
+
     .. change::
       :tags: bug, autogenerate
       :tickets: 318
diff --git a/tests/test_autogen_render.py b/tests/test_autogen_render.py
index 989fe4be..e7010b5a 100644
--- a/tests/test_autogen_render.py
+++ b/tests/test_autogen_render.py
@@ -1058,6 +1058,16 @@ unique=False, """
             "existing_type=sa.Integer(), nullable=True)"
         )
 
+    def test_render_modify_nullable_no_existing_type(self):
+        op_obj = ops.AlterColumnOp(
+            "sometable", "somecolumn",
+            modify_nullable=True
+        )
+        eq_ignore_whitespace(
+            autogenerate.render_op_text(self.autogen_context, op_obj),
+            "op.alter_column('sometable', 'somecolumn', nullable=True)"
+        )
+
     def test_render_modify_nullable_w_schema(self):
         op_obj = ops.AlterColumnOp(
             "sometable", "somecolumn",
-- 
2.47.2