1. 将URL中的默认值使用三目运算符表示。

[andyqian]

What is the purpose of the change

将URL类中的默认值，修改为用三目运算符使用。减少冗余代码！

Brief changelog

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[codecov-io]

Codecov Report

Merging #4301 into master will increase coverage by 0.01%.
The diff coverage is 30.43%.

@@             Coverage Diff              @@
##             master    #4301      +/-   ##
============================================
+ Coverage     62.94%   62.95%   +0.01%     
+ Complexity      506      504       -2     
============================================
  Files           769      769              
  Lines         33041    32995      -46     
  Branches       5215     5215              
============================================
- Hits          20798    20773      -25     
+ Misses         9850     9821      -29     
- Partials       2393     2401       +8

Impacted Files	Coverage Δ	Complexity Δ
...mon/src/main/java/org/apache/dubbo/common/URL.java	49.4% <30.43%> (-0.6%)	0 <0> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	80.07% <0%> (-1.54%)	0% <0%> (ø)
...ache/dubbo/registry/multiple/MultipleRegistry.java	62.67% <0%> (-1.41%)	20% <0%> (-2%)
...pache/dubbo/remoting/transport/AbstractServer.java	47.91% <0%> (-1.05%)	0% <0%> (ø)
...g/apache/dubbo/registry/consul/ConsulRegistry.java	59.6% <0%> (-0.67%)	27% <0%> (ø)
...ting/zookeeper/curator/CuratorZookeeperClient.java	64.15% <0%> (+1.25%)	0% <0%> (ø)	⬇️
...he/dubbo/registry/multicast/MulticastRegistry.java	69.23% <0%> (+1.35%)	0% <0%> (ø)	⬇️
.../apache/dubbo/remoting/transport/AbstractPeer.java	67.39% <0%> (+2.17%)	0% <0%> (ø)	⬇️
.../remoting/transport/netty4/NettyServerHandler.java	71.42% <0%> (+9.52%)	0% <0%> (ø)	⬇️

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[lixiaojiee]

It looks good to me, thank you for your contribution.