优化sip消息构建，去除ServerTransaction的使用

src/main/java/com/genersoft/iot/vmp/utils/GitUtil.java

@@ -11,22 +11,22 @@ import org.springframework.stereotype.Component;
 @PropertySource(value = {"classpath:git.properties" }, ignoreResourceNotFound = true)
 public class GitUtil {
 
-    @Value("${git.branch:null}")
+    @Value("${git.branch:}")
     private String branch;
-    @Value("${git.commit.id:null}")
+    @Value("${git.commit.id:}")
     private String gitCommitId;
-    @Value("${git.remote.origin.url:null}")
+    @Value("${git.remote.origin.url:}")
     private String gitUrl;
-    @Value("${git.build.time:null}")
+    @Value("${git.build.time:}")
     private String buildDate;
 
-    @Value("${git.build.version:null}")
+    @Value("${git.build.version:}")
     private String buildVersion;
 
-    @Value("${git.commit.id.abbrev:null}")
+    @Value("${git.commit.id.abbrev:}")
     private String commitIdShort;
 
-    @Value("${git.commit.time:null}")
+    @Value("${git.commit.time:}")
     private String commitTime;
 
     public String getGitCommitId() {