Make ofxsource.bankid nullable

Turns out that the bank I picked first, AFCU, has a bankid. Not all
institutions have one

alembic/versions/3bac184298c9_nullable_bankid.py

@@ -0,0 +1,28 @@
+"""nullable_bankid
+
+Revision ID: 3bac184298c9
+Revises: a5eaf1296414
+Create Date: 2016-07-20 15:33:20.377382
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '3bac184298c9'
+down_revision = 'a5eaf1296414'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+def upgrade():
+    op.alter_column('ofxsource', 'bankid',
+               existing_type=sa.VARCHAR(length=255),
+               nullable=True)
+
+
+def downgrade():
+    op.alter_column('ofxsource', 'bankid',
+               existing_type=sa.VARCHAR(length=255),
+               nullable=False)