Fix bugs in model

apps/map/migrations/0040_auto_20180328_0309.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.6 on 2018-03-28 03:09
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('map', '0039_auto_20180328_0245'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='casestudy',
+            name='type_of_extraction',
+            field=models.CharField(blank=True, choices=[('SUR', 'Surface (open pit/open cast/open cut mining)'), ('SUB', 'Sub-surface (underground mining)'), ('SEA', 'Seabed mining'), ('URB', 'Urban mining/recycling')], default=None, max_length=3, null=True, verbose_name='Type of extraction'),
+        ),
+    ]