panel-header: Avoid undefined classNames and use the real panel description

public/app/core/components/Tooltip/withPopper.tsx

@@ -68,6 +68,8 @@ export default function withPopper(WrappedComponent) {
 
     render() {
       const { show, placement } = this.state;
+      const className = this.props.className || '';
+
       return (
         <WrappedComponent
           {...this.props}
@@ -76,6 +78,7 @@ export default function withPopper(WrappedComponent) {
           renderContent={this.renderContent}
           show={show}
           placement={placement}
+          className={className}
         />
       );
     }

public/app/features/dashboard/dashgrid/PanelHeader/PanelHeader.tsx

@@ -42,15 +42,16 @@ export class PanelHeader extends PureComponent<Props, State> {
     const isLoading = false;
     const panelHeaderClass = classNames({ 'panel-header': true, 'grid-drag-handle': !isFullscreen });
     const { panel, dashboard, timeInfo } = this.props;
-    const cornerCssClass = panel.description ? 'panel-info-corner--info' : '';
     return (
       <div className={panelHeaderClass}>
-        <Tooltip content="hello world">
-          <span className={`panel-info-corner ${cornerCssClass}`}>
+        {panel.description && (
+          <Tooltip content={panel.description}>
+            <span className="panel-info-corner panel-info-corner--info">
               <i className="fa" />
               <span className="panel-info-corner-inner" />
             </span>
           </Tooltip>
+        )}
         {isLoading && (
           <span className="panel-loading">
             <i className="fa fa-spinner fa-spin" />