Make sure MetabaseUtils.isEmpty() disallows blank strings

frontend/src/metabase/lib/utils.js

@@ -37,7 +37,7 @@ var MetabaseUtils = {
     },
 
     isEmpty: function(str) {
-        return (str == null || 0 === str.length);
+        return (str == null || 0 === str.length || str.match(/^\s+$/));
     },
 
     // pretty limited.  just does 0-9 for right now.

frontend/test/lib/utils.unit.spec.js

@@ -71,7 +71,13 @@ describe('utils', () => {
             shuffle(shuffled);
             shuffled.sort(MetabaseUtils.compareVersions);
             expect(shuffled).toEqual(expected);
-        })
+        });
+    });
+
+    describe("isEmpty" () => {
+        it("should not allow all-blank strings", () => {
+            expect(MetabaseUtils.isEmpty(" ")).toEqual(true);
+        });
     })
 });