feat: add null safety for tracer initialization and update tests

Author: diegomarquezp

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/SpanTracerFactory.java

@@ -103,9 +103,18 @@ public ApiTracerContext getApiTracerContext() {
    */
   @Override
   public ApiTracerFactory withContext(ApiTracerContext context) {
+		if (context == null) {
+			return new BaseApiTracerFactory();
+		}
     ApiTracerContext mergedContext = this.apiTracerContext.merge(context);
     LibraryMetadata metadata = mergedContext.libraryMetadata();
+		if (metadata == null) {
+			return new BaseApiTracerFactory();
+		}
     Tracer newTracer = openTelemetry.getTracer(metadata.artifactName(), metadata.version());
+		if (newTracer == null) {
+			return new BaseApiTracerFactory();
+		}
     return new SpanTracerFactory(openTelemetry, newTracer, mergedContext);
   }
 }

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/SpanTracerFactoryTest.java

@@ -173,7 +173,10 @@ void testWithContext_addsInferredAttributes(boolean useContext) {
   @ParameterizedTest
   @ValueSource(booleans = {false, true})
   void testWithContext_noEndpointContext_doesNotAddServerAddressAttribute(boolean useContext) {
-    ApiTracerContext context = ApiTracerContext.empty();
+    ApiTracerContext context =
+        ApiTracerContext.newBuilder()
+            .setLibraryMetadata(LibraryMetadata.empty())
+            .build();
 
     SpanTracerFactory factory =
         new SpanTracerFactory(openTelemetry, tracer, ApiTracerContext.empty());
@@ -322,4 +325,37 @@ void testNoOpWhenTracerNull() {
 
     assertThat(tracerInstance2).isInstanceOf(BaseApiTracer.class);
   }
+
+  @Test
+  void testWithContext_nullContext_returnsBaseApiTracerFactory() {
+    SpanTracerFactory factory =
+        new SpanTracerFactory(openTelemetry, tracer, ApiTracerContext.empty());
+    ApiTracerFactory factoryWithContext = factory.withContext(null);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_nullMetadata_returnsBaseApiTracerFactory() {
+    SpanTracerFactory factory =
+        new SpanTracerFactory(openTelemetry, tracer, ApiTracerContext.empty());
+    // Assuming ApiTracerContext.empty() has null libraryMetadata
+    ApiTracerFactory factoryWithContext = factory.withContext(ApiTracerContext.empty());
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
+
+  @Test
+  void testWithContext_nullTracer_returnsBaseApiTracerFactory() {
+    OpenTelemetry mockOpenTelemetry = mock(OpenTelemetry.class);
+    when(mockOpenTelemetry.getTracer(nullable(String.class), nullable(String.class))).thenReturn(null);
+
+    SpanTracerFactory factory =
+        new SpanTracerFactory(mockOpenTelemetry, tracer, ApiTracerContext.empty());
+    ApiTracerContext context =
+        ApiTracerContext.newBuilder()
+            .setLibraryMetadata(LibraryMetadata.empty())
+            .build();
+
+    ApiTracerFactory factoryWithContext = factory.withContext(context);
+    assertThat(factoryWithContext).isInstanceOf(BaseApiTracerFactory.class);
+  }
 }