1. add getter getHasBranchFilter() in GogsProjectProperty, used in config.jelly to set branch filter check status;

2. remove default value of branch filter

Author: chenz85

src/main/java/org/jenkinsci/plugins/gogs/GogsProjectProperty.java

@@ -58,6 +58,10 @@ public String getGogsBranchFilter() {
         return this.gogsBranchFilter;
     }
 
+    public boolean getHasBranchFilter() {
+        return gogsBranchFilter != null && gogsBranchFilter.length() > 0;
+    }
+
     private static final Logger LOGGER = Logger.getLogger(GogsWebHook.class.getName());
 
     @Extension

src/main/resources/org/jenkinsci/plugins/gogs/GogsProjectProperty/config.jelly

@@ -6,9 +6,9 @@
         <f:password field="gogsSecret" />
       </f:entry>
     </f:optionalBlock>
-    <f:optionalBlock title="Branch Filter" inline="true" checked="${instance.gogsBranchFilter != null}">
-      <f:entry title="${%BranchFilter}" description="default: master">
-        <f:textbox default="master" field="gogsBranchFilter" />
+    <f:optionalBlock title="Branch Filter" inline="true" checked="${instance.hasBranchFilter}">
+      <f:entry title="${%BranchFilter}">
+        <f:textbox field="gogsBranchFilter" />
       </f:entry>
     </f:optionalBlock>
   </f:section>