Fix issue that made empty string attribute values trigger changedCallback instead of disconnectedCallback removing an attribute

Author: trusktr

attr.js

@@ -120,7 +120,7 @@ class CustomAttributeRegistry {
       }
     }
     // Attribute was removed
-    else if(newVal == null && !!inst.value) {
+    else if(newVal == null) {
       inst.value = newVal;
       if(inst.disconnectedCallback) {
         inst.disconnectedCallback();

registry.js

@@ -117,7 +117,7 @@ class CustomAttributeRegistry {
       }
     }
     // Attribute was removed
-    else if(newVal == null && !!inst.value) {
+    else if(newVal == null) {
       inst.value = newVal;
       if(inst.disconnectedCallback) {
         inst.disconnectedCallback();