Fix GitLab issue #250 "Empty optional lookup metadata trigger validation error". Thanks to LeVon Smoker for the find and for the proposed fix.

Reference: https://groups.google.com/forum/#!topic/mayan-edms/VUGRl4xX-1c

mayan/apps/metadata/models.py

@@ -126,7 +126,7 @@ class MetadataType(models.Model):
 
         if self.lookup:
             lookup_options = self.get_lookup_values()
-            if value not in lookup_options:
+            if value and value not in lookup_options:
                 raise ValidationError(
                     _('Value is not one of the provided options.')
                 )

mayan/apps/metadata/tests/test_models.py

@@ -63,8 +63,9 @@ class MetadataTestCase(TestCase):
             self.document.metadata_value_of.test, TEST_DEFAULT_VALUE
         )
 
-    def test_lookup(self):
+    def test_lookup_with_incorrect_value(self):
         self.metadata_type.lookup = TEST_LOOKUP_TEMPLATE
+        self.metadata_type.save()
 
         document_metadata = DocumentMetadata(
             document=self.document, metadata_type=self.metadata_type,
@@ -76,8 +77,15 @@ class MetadataTestCase(TestCase):
             document_metadata.full_clean()
             document_metadata.save()
 
-        # Should not return error
-        document_metadata.value = TEST_CORRECT_LOOKUP_VALUE
+    def test_lookup_with_correct_value(self):
+        self.metadata_type.lookup = TEST_LOOKUP_TEMPLATE
+        self.metadata_type.save()
+
+        document_metadata = DocumentMetadata(
+            document=self.document, metadata_type=self.metadata_type,
+            value=TEST_CORRECT_LOOKUP_VALUE
+        )
+
         document_metadata.full_clean()
         document_metadata.save()
 
@@ -85,6 +93,22 @@ class MetadataTestCase(TestCase):
             self.document.metadata_value_of.test, TEST_CORRECT_LOOKUP_VALUE
         )
 
+    def test_empty_optional_lookup(self):
+        """
+        Checks for GitLab issue #250
+        Empty optional lookup metadata trigger validation error
+        """
+
+        self.metadata_type.lookup = TEST_LOOKUP_TEMPLATE
+        self.metadata_type.save()
+
+        document_metadata = DocumentMetadata(
+            document=self.document, metadata_type=self.metadata_type
+        )
+
+        document_metadata.full_clean()
+        document_metadata.save()
+
     def test_validation(self):
         self.metadata_type.validation = TEST_DATE_VALIDATOR