Removed the - signs from default spring var resolution

with the current setup we're using the MDC's default interpolation as a default for spring var resolution (which makes no sense)
with this change we're removing the dashes

fixes gh-1396

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/autoconfig/TraceEnvironmentPostProcessor.java

@@ -49,7 +49,7 @@ public class TraceEnvironmentPostProcessor implements EnvironmentPostProcessor {
 		if (Boolean
 				.parseBoolean(environment.getProperty("spring.sleuth.enabled", "true"))) {
 			map.put("logging.pattern.level", "%5p [${spring.zipkin.service.name:"
-					+ "${spring.application.name:-}},%X{X-B3-TraceId:-},%X{X-B3-SpanId:-},%X{X-Span-Export:-}]");
+					+ "${spring.application.name:}},%X{X-B3-TraceId:-},%X{X-B3-SpanId:-},%X{X-Span-Export:-}]");
 		}
 		addOrReplace(environment.getPropertySources(), map);
 	}

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-feign/src/main/resources/application.yml

@@ -6,7 +6,3 @@ logging.level.com.netflix.discovery: 'OFF'
 sample:
   zipkin:
     enabled: false
-
-spring:
-  application:
-    name: testSleuthFeign

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-feign/src/test/java/sample/SampleFeignApplicationTests.java

@@ -16,10 +16,15 @@
 
 package sample;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.assertj.core.api.BDDAssertions;
+import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.rule.OutputCapture;
 import org.springframework.test.context.TestPropertySource;
 import org.springframework.test.context.junit4.SpringRunner;
 
@@ -28,8 +33,21 @@ import org.springframework.test.context.junit4.SpringRunner;
 @TestPropertySource(properties = "sample.zipkin.enabled=false")
 public class SampleFeignApplicationTests {
 
+	private static final Log log = LogFactory.getLog(SampleFeignApplicationTests.class);
+
+	@Rule
+	public OutputCapture outputCapture = new OutputCapture();
+
 	@Test
 	public void contextLoads() {
 	}
 
+	// https://github.com/spring-cloud/spring-cloud-sleuth/issues/1396
+	@Test
+	public void should_not_pass_dash_as_default_service_name() {
+		log.info("HELLO");
+
+		BDDAssertions.then(this.outputCapture.toString()).doesNotContain("INFO [-,,,]");
+	}
+
 }