Fix errors on empty config and config sections

This commit fixes the rest of issue #22

features/config.feature

@@ -1,6 +1,29 @@
 Feature: Getting info from config
 
+    Scenario: Empty config
+        Given migration dir
+        And migrations
+           | file                     | code      |
+           | V1__Single_migration.sql | SELECT 1; |
+        And empty config
+        And database and connection
+        When we run pgmigrate with "-t 1 migrate"
+        Then pgmigrate command "succeeded"
+
     Scenario: Empty callbacks in config
+        Given migration dir
+        And migrations
+           | file                     | code      |
+           | V1__Single_migration.sql | SELECT 1; |
+        And config
+        """
+        callbacks:
+        """
+        And database and connection
+        When we run pgmigrate with "-t 1 migrate"
+        Then pgmigrate command "succeeded"
+
+    Scenario: Empty callbacks lists in config
         Given migration dir
         And migrations
            | file                     | code      |
@@ -17,6 +40,15 @@ Feature: Getting info from config
         When we run pgmigrate with "-t 1 migrate"
         Then pgmigrate command "succeeded"
 
+    Scenario: Empty callbacks lists in args
+        Given migration dir
+        And migrations
+           | file                     | code      |
+           | V1__Single_migration.sql | SELECT 1; |
+        And database and connection
+        When we run pgmigrate with "-a ,,,, -t 1 migrate"
+        Then pgmigrate command "succeeded"
+
     Scenario: Callbacks from config are executed in correct order
         Given migration dir
         And migrations
@@ -93,3 +125,4 @@ Feature: Getting info from config
            | version | installed_by |
            | 1       | postgres     |
            | 2       | test_user    |
+

features/steps/config.py

@@ -1,3 +1,5 @@
+import os
+
 import yaml
 
 from behave import given
@@ -7,3 +9,8 @@ from behave import given
 def step_impl(context):
     data = yaml.safe_load(context.text)
     context.migrate_config = data
+
+
+@given('empty config')  # noqa
+def step_impl(context):
+    open(os.path.join(context.migr_dir, 'migrations.yml'), 'w').close()

pgmigrate.py

@@ -471,6 +471,8 @@ def _apply_version(version, base_dir, user, schema, cursor):
 
 
 def _parse_str_callbacks(callbacks, ret, base_dir):
+    if not callbacks:
+        return ret
     callbacks = callbacks.split(',')
     for callback in callbacks:
         if not callback:
@@ -787,7 +789,7 @@ def get_config(base_dir, args=None):
     path = os.path.join(base_dir, 'migrations.yml')
     try:
         with codecs.open(path, encoding='utf-8') as i:
-            base = yaml.safe_load(i)
+            base = yaml.safe_load(i) or {}
     except IOError:
         LOG.info('Unable to load %s. Using defaults', path)
         base = {}