Improved fix for #7270

core/modules/widgets/let.js

@@ -53,7 +53,9 @@ LetWidget.prototype.computeAttributes = function() {
 			name = attribute.name;
 		// Now that it's prepped, we're allowed to look this variable up
 		// when defining later variables
-		self.currentValueFor[name] = value;
+		if(value !== undefined) {
+			self.currentValueFor[name] = value;
+		}
 	});
 	// Run through again, setting variables and looking for differences
 	$tw.utils.each(this.currentValueFor,function(value,name) {

editions/test/tiddlers/tests/data/widgets/LetWidgetUndefinedVariable.tid

@@ -0,0 +1,15 @@
+title: Widgets/LetWidgetUndefinedVariable
+description: Test let widget undefined variable
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\whitespace trim
+<$let test1=<<test>> test2={{{ [<test1>] }}}>
+<<test2>>
+</$let>
++
+title: ExpectedResult
+
+<p></p>