[APOLLO-2015]: fix bug that cannot resolve blank line in properties under Windows (#2017)

* bugfix: line feed under Windows. resolve issue #2015

apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolver.java

@@ -5,6 +5,7 @@ import com.ctrip.framework.apollo.common.dto.ItemDTO;
 import com.ctrip.framework.apollo.common.exception.BadRequestException;
 import com.ctrip.framework.apollo.common.utils.BeanUtils;
 
+import com.google.common.base.Strings;
 import org.springframework.stereotype.Component;
 
 import java.util.HashMap;
@@ -155,7 +156,7 @@ public class PropertyResolver implements ConfigTextResolver {
   }
 
   private boolean isBlankItem(String line) {
-    return "".equals(line);
+    return  Strings.nullToEmpty(line).trim().isEmpty();
   }
 
   private void deleteNormalKVItem(Map<String, ItemDTO> baseKeyMapItem, ItemChangeSets changeSets) {