support NONE value in Level component

server/sonar-web/src/main/js/components/ui/Level.css

@@ -47,3 +47,7 @@ a > .level:hover {
 .level-ERROR {
   background-color: #d4333f;
 }
+
+.level-NONE {
+  background-color: #b4b4b4;
+}

server/sonar-web/src/main/js/components/ui/Level.js

@@ -26,7 +26,7 @@ import './Level.css';
 export default class Level extends React.PureComponent {
   static propTypes = {
     className: PropTypes.string,
-    level: PropTypes.oneOf(['ERROR', 'WARN', 'OK']).isRequired,
+    level: PropTypes.oneOf(['ERROR', 'WARN', 'OK', 'NONE']).isRequired,
     small: PropTypes.bool,
     muted: PropTypes.bool
   };

sonar-core/src/main/resources/org/sonar/l10n/core.properties

@@ -2052,6 +2052,7 @@ metric.type.WORK_DUR=Work Duration
 metric.level.ERROR=Failed
 metric.level.WARN=Warning
 metric.level.OK=Passed
+metric.level.NONE=None
 
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