diff --git a/swh/graphql/resolvers/snapshot_branch.py b/swh/graphql/resolvers/snapshot_branch.py
--- a/swh/graphql/resolvers/snapshot_branch.py
+++ b/swh/graphql/resolvers/snapshot_branch.py
@@ -3,10 +3,11 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-from collections import namedtuple
+from typing import Optional, Tuple
 
-from swh.graphql.errors import ObjectNotFoundError
+from swh.graphql.errors import DataError
 from swh.graphql.utils import utils
+from swh.model.model import SnapshotBranch
 from swh.storage.interface import PagedResult
 
 from .base_connection import BaseConnection
@@ -18,17 +19,21 @@
     # target field for this node is a UNION type
     # It is resolved in the top level (resolvers.resolvers.py)
 
-    def _get_node_from_data(self, node_data: tuple):
-        # node_data is a tuple as returned by _get_paged_result in
-        # SnapshotBranchConnection and _get_node_data in AliasSnapshotBranchNode
-        # overriding to support this special data structure
-        branch_name, branch_obj = node_data
-        node = {
-            "name": branch_name,
-            "type": branch_obj.target_type.value,
-            "target_hash": branch_obj.target,
-        }
-        return namedtuple("NodeObj", node.keys())(*node.values())
+    def _get_node_from_data(
+        self, node_data: Optional[Tuple[bytes, Optional[SnapshotBranch]]]
+    ):
+        # node_data is received as a tuple from the archive
+        # (unlike an object or a dict in other cases)
+        # override this method to make a dict from this special data structure
+        structured_node_data = None
+        if node_data is not None:
+            branch_name, branch_obj = node_data
+            structured_node_data = {
+                "name": branch_name,
+                "type": branch_obj.target_type.value if branch_obj else None,
+                "target_hash": branch_obj.target if branch_obj else None,
+            }
+        return super()._get_node_from_data(structured_node_data)
 
     def is_type_of(self):
         return "Branch"
@@ -56,25 +61,27 @@
                 return parent.swhid
             parent = parent.obj
         # Reached the root query node. This will never happen with the current entrypoints
-        raise ObjectNotFoundError("There is no snapshot associated with the branch")
+        # raise a DataError in this case
+        raise DataError(
+            f"Missing snapshot for the branch {self.target_hash}, last known parent is {parent}"
+        )
 
 
 class AliasSnapshotBranchNode(BaseSnapshotBranchNode):
 
+    _can_be_null = True
     obj: BaseSnapshotBranchNode
 
     def _get_node_data(self):
+        target_branch: Optional[bytes] = self.obj.target_hash
         snapshot_swhid = self.snapshot_swhid()
-        target_branch = self.obj.target_hash
-
         alias_branch = self.archive.get_snapshot_branches(
             snapshot_swhid.object_id, first=1, name_include=target_branch
         )
         if target_branch not in alias_branch["branches"]:
-            raise ObjectNotFoundError(
-                f"Branch name with {target_branch.decode()} is not available"
-            )
-        # this will be serialized in _get_node_from_data method in the base class
+            # FIXME, alias branch is missing, log this event
+            return None
+        # this will be converted to a dict in _get_node_from_data method in the base class
         return (target_branch, alias_branch["branches"][target_branch])
 
 
@@ -106,7 +113,8 @@
         # FIX in swh-storage to return PagedResult
         # STORAGE-TODO
 
-        # this will be serialized in _get_node_from_data method in the node class
+        # each result item will be converted to a dict in _get_node_from_data method
+        # in the node class
         return PagedResult(
             results=result["branches"].items(), next_page_token=end_cusrsor
         )
diff --git a/swh/graphql/tests/data.py b/swh/graphql/tests/data.py
--- a/swh/graphql/tests/data.py
+++ b/swh/graphql/tests/data.py
@@ -13,6 +13,9 @@
     Release,
     Revision,
     RevisionType,
+    Snapshot,
+    SnapshotBranch,
+    TargetType,
 )
 from swh.model.tests import swh_model_data
 
@@ -172,7 +175,20 @@
     ]
 
 
+def get_snapshots_with_missing_alias():
+    return [
+        Snapshot(
+            branches={
+                b"target/missing-alias": SnapshotBranch(
+                    target_type=TargetType.ALIAS, target=b"target/revision"
+                ),
+            },
+        ),
+    ]
+
+
 GRAPHQL_EXTRA_TEST_OBJECTS = {
+    "snapshot": get_snapshots_with_missing_alias(),
     "release": get_releases_with_target(),
     "revision": get_revisions_with_parents() + get_revisions_with_none_date(),
     "directory": get_directories_with_nested_path()
diff --git a/swh/graphql/tests/functional/test_branch_connection.py b/swh/graphql/tests/functional/test_branch_connection.py
--- a/swh/graphql/tests/functional/test_branch_connection.py
+++ b/swh/graphql/tests/functional/test_branch_connection.py
@@ -6,6 +6,7 @@
 import pytest
 
 from . import utils
+from ..data import get_snapshots_with_missing_alias
 
 
 def get_branches(client, **kwargs) -> tuple:
@@ -81,6 +82,20 @@
     }
 
 
+@pytest.mark.parametrize("snapshot", get_snapshots_with_missing_alias())
+def test_get_branches_with_missing_alias(client, snapshot):
+    data, errors = get_branches(
+        client, swhid=str(snapshot.swhid()), first=1, types=["alias"]
+    )
+    node = data["snapshot"]["branches"]["nodes"][0]
+    assert errors is None
+    assert node == {
+        "name": {"text": "target/missing-alias"},
+        "target": None,
+        "targetType": "alias",
+    }
+
+
 @pytest.mark.parametrize(
     "filter_type, count, target_type, swhid_pattern",
     [