diff --git a/apps/opik-backend/src/main/java/com/comet/opik/domain/llmproviders/LlmProviderFactory.java b/apps/opik-backend/src/main/java/com/comet/opik/domain/llmproviders/LlmProviderFactory.java
index 2d81f1412e..130a355197 100644
--- a/apps/opik-backend/src/main/java/com/comet/opik/domain/llmproviders/LlmProviderFactory.java
+++ b/apps/opik-backend/src/main/java/com/comet/opik/domain/llmproviders/LlmProviderFactory.java
@@ -17,6 +17,8 @@
 
 @Singleton
 public class LlmProviderFactory {
+    public static final String ERROR_MODEL_NOT_SUPPORTED = "model not supported %s";
+
     private final LlmProviderClientConfig llmProviderClientConfig;
     private final LlmProviderApiKeyService llmProviderApiKeyService;
 
@@ -52,7 +54,7 @@ private LlmProvider getLlmProvider(String model) {
             return LlmProvider.ANTHROPIC;
         }
 
-        throw new BadRequestException("model not supported: " + model);
+        throw new BadRequestException(ERROR_MODEL_NOT_SUPPORTED.formatted(model));
     }
 
     /**
diff --git a/apps/opik-backend/src/test/java/com/comet/opik/api/resources/v1/priv/ChatCompletionsResourceTest.java b/apps/opik-backend/src/test/java/com/comet/opik/api/resources/v1/priv/ChatCompletionsResourceTest.java
index 426f895eed..b487b11f96 100644
--- a/apps/opik-backend/src/test/java/com/comet/opik/api/resources/v1/priv/ChatCompletionsResourceTest.java
+++ b/apps/opik-backend/src/test/java/com/comet/opik/api/resources/v1/priv/ChatCompletionsResourceTest.java
@@ -27,7 +27,6 @@
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
-import org.junit.jupiter.params.provider.NullSource;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.testcontainers.clickhouse.ClickHouseContainer;
 import org.testcontainers.containers.MySQLContainer;
@@ -41,6 +40,7 @@
 import java.util.UUID;
 import java.util.stream.Stream;
 
+import static com.comet.opik.domain.llmproviders.LlmProviderFactory.ERROR_MODEL_NOT_SUPPORTED;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assumptions.assumeThat;
 
@@ -154,7 +154,6 @@ void createReturnsBadRequestWhenNoLlmProviderApiKey() {
 
         @ParameterizedTest
         @ValueSource(strings = {"", "non-existing-model"})
-        @NullSource
         void createReturnsBadRequestWhenModelIsInvalid(String model) {
             var workspaceName = RandomStringUtils.randomAlphanumeric(20);
             var workspaceId = UUID.randomUUID().toString();
@@ -171,7 +170,7 @@ void createReturnsBadRequestWhenModelIsInvalid(String model) {
 
             assertThat(errorMessage.getCode()).isEqualTo(HttpStatus.SC_BAD_REQUEST);
             assertThat(errorMessage.getMessage())
-                    .containsIgnoringCase("invalid model '%s'".formatted(model));
+                    .containsIgnoringCase(ERROR_MODEL_NOT_SUPPORTED.formatted(model));
         }
 
         @ParameterizedTest