diff --git a/exabel_data_sdk/client/api/entity_api.py b/exabel_data_sdk/client/api/entity_api.py
index 665d6b7..4021687 100644
--- a/exabel_data_sdk/client/api/entity_api.py
+++ b/exabel_data_sdk/client/api/entity_api.py
@@ -1,4 +1,4 @@
-from typing import Sequence
+from typing import Optional, Sequence
 
 from exabel_data_sdk.client.api.api_client.grpc.entity_grpc_client import EntityGrpcClient
 from exabel_data_sdk.client.api.api_client.http.entity_http_client import EntityHttpClient
@@ -48,15 +48,22 @@ def list_entity_types(
             total_size=response.total_size,
         )
 
-    def get_entity_type(self, name: str) -> EntityType:
+    def get_entity_type(self, name: str) -> Optional[EntityType]:
         """
         Get one entity type.
 
+        Return None if the entity type does not exist.
+
         Args:
             name:   The resource name of the requested entity type, for example
                     "entityTypes/ns.type1".
         """
-        response = self.client.get_entity_type(GetEntityTypeRequest(name=name))
+        try:
+            response = self.client.get_entity_type(GetEntityTypeRequest(name=name))
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
         return EntityType.from_proto(response)
 
     def list_entities(
@@ -81,15 +88,22 @@ def list_entities(
             total_size=response.total_size,
         )
 
-    def get_entity(self, name: str) -> Entity:
+    def get_entity(self, name: str) -> Optional[Entity]:
         """
         Get one entity.
 
+        Return None if the entity does not exist.
+
         Args:
             name:   The resource name of the requested entity, for example
                     "entityTypes/ns.type1/entities/ns.entity1".
         """
-        response = self.client.get_entity(GetEntityRequest(name=name))
+        try:
+            response = self.client.get_entity(GetEntityRequest(name=name))
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
         return Entity.from_proto(response)
 
     def create_entity(self, entity: Entity, entity_type: str) -> Entity:
@@ -141,10 +155,4 @@ def entity_exists(self, name: str) -> bool:
             name:   The resource name of the entity,
                     for example "entityTypes/ns.type1/entities/ns.entity1".
         """
-        try:
-            self.get_entity(name)
-            return True
-        except RequestError as error:
-            if error.error_type is ErrorType.NOT_FOUND:
-                return False
-            raise
+        return self.get_entity(name) is not None
diff --git a/exabel_data_sdk/client/api/relationship_api.py b/exabel_data_sdk/client/api/relationship_api.py
index a7a3f94..29a98ff 100644
--- a/exabel_data_sdk/client/api/relationship_api.py
+++ b/exabel_data_sdk/client/api/relationship_api.py
@@ -1,3 +1,5 @@
+from typing import Optional
+
 from exabel_data_sdk.client.api.api_client.grpc.relationship_grpc_client import (
     RelationshipGrpcClient,
 )
@@ -49,15 +51,22 @@ def list_relationship_types(
             total_size=response.total_size,
         )
 
-    def get_relationship_type(self, name: str) -> RelationshipType:
+    def get_relationship_type(self, name: str) -> Optional[RelationshipType]:
         """
         Get one relationship type.
 
+        Return None if the relationship type does not exist.
+
         Args:
             name:   The resource name of the requested relationship type, for example
                     "relationshipTypes/ns.type1"
         """
-        response = self.client.get_relationship_type(GetRelationshipTypeRequest(name=name))
+        try:
+            response = self.client.get_relationship_type(GetRelationshipTypeRequest(name=name))
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
         return RelationshipType.from_proto(response)
 
     def create_relationship_type(self, relationship_type: RelationshipType) -> RelationshipType:
@@ -153,10 +162,12 @@ def get_relationships_to_entity(
 
     def get_relationship(
         self, relationship_type: str, from_entity: str, to_entity: str
-    ) -> Relationship:
+    ) -> Optional[Relationship]:
         """
         Get one relationship.
 
+        Return None if the relationship does not exist.
+
         Args:
             relationship_type:  The type of the relationship, for example
                                 "relationshipTypes/ns.type1".
@@ -165,11 +176,16 @@ def get_relationship(
             to_entity:          The resource name of the end point of the relationship, for example
                                 "entityTypes/ns.type2/entities/ns.entity2".
         """
-        response = self.client.get_relationship(
-            GetRelationshipRequest(
-                parent=relationship_type, from_entity=from_entity, to_entity=to_entity
+        try:
+            response = self.client.get_relationship(
+                GetRelationshipRequest(
+                    parent=relationship_type, from_entity=from_entity, to_entity=to_entity
+                )
             )
-        )
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
         return Relationship.from_proto(response)
 
     def create_relationship(self, relationship: Relationship) -> Relationship:
@@ -212,10 +228,4 @@ def relationship_exists(self, relationship_type: str, from_entity: str, to_entit
             to_entity:          The resource name of the end point of the relationship,
                                 for example "entityTypes/ns.type2/entities/ns.entity2".
         """
-        try:
-            self.get_relationship(relationship_type, from_entity, to_entity)
-            return True
-        except RequestError as error:
-            if error.error_type is ErrorType.NOT_FOUND:
-                return False
-            raise
+        return self.get_relationship(relationship_type, from_entity, to_entity) is not None
diff --git a/exabel_data_sdk/client/api/signal_api.py b/exabel_data_sdk/client/api/signal_api.py
index 07e67a3..5852895 100644
--- a/exabel_data_sdk/client/api/signal_api.py
+++ b/exabel_data_sdk/client/api/signal_api.py
@@ -1,6 +1,9 @@
+from typing import Optional
+
 from exabel_data_sdk.client.api.api_client.grpc.signal_grpc_client import SignalGrpcClient
 from exabel_data_sdk.client.api.api_client.http.signal_http_client import SignalHttpClient
 from exabel_data_sdk.client.api.data_classes.paging_result import PagingResult
+from exabel_data_sdk.client.api.data_classes.request_error import ErrorType, RequestError
 from exabel_data_sdk.client.api.data_classes.signal import Signal
 from exabel_data_sdk.client.client_config import ClientConfig
 from exabel_data_sdk.stubs.exabel.api.data.v1.all_pb2 import (
@@ -37,16 +40,23 @@ def list_signals(self, page_size: int = 1000, page_token: str = None) -> PagingR
             total_size=response.total_size,
         )
 
-    def get_signal(self, name: str) -> Signal:
+    def get_signal(self, name: str) -> Optional[Signal]:
         """
         Get one signal.
 
+        Return None if the signal does not exist.
+
         Args:
             name: The resource name of the requested signal, for example "signals/ns.signal1".
         """
-        response = self.client.get_signal(
-            GetSignalRequest(name=name),
-        )
+        try:
+            response = self.client.get_signal(
+                GetSignalRequest(name=name),
+            )
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
         return Signal.from_proto(response)
 
     def create_signal(self, signal: Signal) -> Signal:
diff --git a/exabel_data_sdk/client/api/time_series_api.py b/exabel_data_sdk/client/api/time_series_api.py
index f956608..afac763 100644
--- a/exabel_data_sdk/client/api/time_series_api.py
+++ b/exabel_data_sdk/client/api/time_series_api.py
@@ -79,13 +79,15 @@ def get_entity_time_series(
 
     def get_time_series(
         self, name: str, start: pd.Timestamp = None, end: pd.Timestamp = None
-    ) -> pd.Series:
+    ) -> Optional[pd.Series]:
         """
         Get one time series.
 
         If start and end are not specified, all data points will be returned.
         If start or end is specified, both must be specified.
 
+        If time series does not exist, None is returned.
+
         Args:
             name:   The resource name of the requested time series, for example
                     "entityTypes/ns.type1/entities/ns.entity1/signals/ns.signal1" or
@@ -96,9 +98,16 @@ def get_time_series(
         if bool(start) != bool(end):
             raise ValueError("Either specify both 'start' and 'end' or none of them.")
         time_range = self._get_time_range(start, end)
-        time_series = self.client.get_time_series(
-            GetTimeSeriesRequest(name=name, view=TimeSeriesView(time_range=time_range)),
-        )
+
+        try:
+            time_series = self.client.get_time_series(
+                GetTimeSeriesRequest(name=name, view=TimeSeriesView(time_range=time_range)),
+            )
+        except RequestError as error:
+            if error.error_type == ErrorType.NOT_FOUND:
+                return None
+            raise
+
         return self._time_series_points_to_series(time_series.points, time_series.name)
 
     def create_time_series(self, name: str, series: pd.Series) -> None:
@@ -205,13 +214,7 @@ def time_series_exists(self, name: str) -> bool:
             name:   The resource name of the time series, for example
                     "entityTypes/ns.type1/entities/ns.entity1/signals/ns.signal1".
         """
-        try:
-            self.get_time_series(name)
-            return True
-        except RequestError as error:
-            if error.error_type is ErrorType.NOT_FOUND:
-                return False
-            raise
+        return self.get_time_series(name) is not None
 
     @staticmethod
     def _series_to_time_series_points(series: pd.Series) -> Sequence[TimeSeriesPoint]:
diff --git a/exabel_data_sdk/examples/create_time_series_example.py b/exabel_data_sdk/examples/create_time_series_example.py
index 4535e2c..9cd9d3d 100644
--- a/exabel_data_sdk/examples/create_time_series_example.py
+++ b/exabel_data_sdk/examples/create_time_series_example.py
@@ -46,6 +46,7 @@ def create_time_series() -> None:
 
     # Add a relationship between a company entity and the brand entity.
     company_entity = client.entity_api.get_entity("entityTypes/company/entities/F_000Q07-E")
+    assert company_entity
     relationship = client.relationship_api.create_relationship(
         Relationship(
             description="Relationship between a company and a brand.",
diff --git a/exabel_data_sdk/examples/get_company_example.py b/exabel_data_sdk/examples/get_company_example.py
index 17db48a..b2325b4 100644
--- a/exabel_data_sdk/examples/get_company_example.py
+++ b/exabel_data_sdk/examples/get_company_example.py
@@ -12,6 +12,7 @@ def get_company() -> None:
 
     # Fetch the company.
     microsoft = client.entity_api.get_entity("entityTypes/company/entities/F_000Q07-E")
+    assert microsoft
 
     # Retrieve location of company.
     located_in_relationships = client.relationship_api.get_relationships_from_entity(
@@ -34,6 +35,7 @@ def get_company() -> None:
     primary_security = client.entity_api.get_entity(
         primary_security_relationships.results[0].to_entity
     )
+    assert primary_security
 
     # Retrieve primary regional for company.
     primary_regional_relationships = client.relationship_api.get_relationships_from_entity(
@@ -43,6 +45,7 @@ def get_company() -> None:
     primary_regional = client.entity_api.get_entity(
         primary_regional_relationships.results[0].to_entity
     )
+    assert primary_regional
 
     # Retrieve primary listing for company.
     primary_listing_relationships = client.relationship_api.get_relationships_from_entity(
@@ -61,6 +64,7 @@ def get_company() -> None:
     # Retrieve all regionals.
     regionals = []
     for security in securities:
+        assert security
         regional_relationships = client.relationship_api.get_relationships_from_entity(
             relationship_type="relationshipTypes/HAS_REGIONAL", from_entity=security.name
         )
@@ -71,6 +75,7 @@ def get_company() -> None:
     # Retrieve all listings.
     listings = []
     for regional in regionals:
+        assert regional
         listing_relationships = client.relationship_api.get_relationships_from_entity(
             relationship_type="relationshipTypes/HAS_LISTING", from_entity=regional.name
         )
diff --git a/exabel_data_sdk/scripts/delete_entity.py b/exabel_data_sdk/scripts/delete_entity.py
index 190dbcb..fb1b7f2 100644
--- a/exabel_data_sdk/scripts/delete_entity.py
+++ b/exabel_data_sdk/scripts/delete_entity.py
@@ -32,7 +32,9 @@ def run_script(self, client: ExabelClient, args: argparse.Namespace) -> None:
             print("Running dry-run...")
 
         entity = client.entity_api.get_entity(args.entity_name)
-        if entity.read_only:
+        if entity is None:
+            print(f"Entity does not exist: {entity}")
+        elif entity.read_only:
             print(f"ERROR: Entity is read-only: {entity}")
         else:
             if args.dry_run:
diff --git a/setup.py b/setup.py
index 46eacef..340f91c 100644
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name="exabel-data-sdk",
-    version="0.0.14",
+    version="0.0.15",
     author="Exabel",
     author_email="support@exabel.com",
     description="Python SDK for the Exabel Data API",