fix(tooltip): tooltip-html should not open if empty

Closes #3563

src/tooltip/test/tooltip.spec.js

@@ -528,6 +528,13 @@ describe( 'tooltipHtml', function() {
     expect( elmBody.find('.tooltip-inner').html() ).toBe( scope.html );
   }));
 
+  it( 'should not open if html is empty', function () {
+    scope.safeHtml = null;
+    scope.$digest();
+    elm.trigger( 'mouseenter' );
+    expect( tooltipScope.isOpen ).toBe( false );
+  });
+
   it( 'should show on mouseenter and hide on mouseleave', inject( function ($sce) {
     expect( tooltipScope.isOpen ).toBe( false );
 

src/tooltip/tooltip.js

@@ -500,7 +500,9 @@ function ($animate ,  $sce ,  $compile ,  $templateRequest) {
 })
 
 .directive( 'tooltipHtml', [ '$tooltip', function ( $tooltip ) {
-  return $tooltip( 'tooltipHtml', 'tooltip', 'mouseenter' );
+  return $tooltip('tooltipHtml', 'tooltip', 'mouseenter', {
+    useContentExp: true
+  });
 }])
 
 /*