From d58eec47c07d92bb9c592eecd70f3d8dfb75e219 Mon Sep 17 00:00:00 2001
From: yaisog <m@rcuswinter.de>
Date: Wed, 29 Oct 2025 12:57:39 +0100
Subject: [PATCH] Modify output of some math operators for empty inputs (#9337)

* Initial commit

* Adapt test to new behavior
---
 core/modules/filters/math.js                         | 4 ++++
 editions/test/tiddlers/tests/test-prefixes-filter.js | 4 ++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/core/modules/filters/math.js b/core/modules/filters/math.js
index 4c2a9168a6..bdf2117eb7 100644
--- a/core/modules/filters/math.js
+++ b/core/modules/filters/math.js
@@ -217,6 +217,10 @@ function makeNumericReducingOperator(fnCalc,initialValue,fnFinal) {
 		source(function(tiddler,title) {
 			result.push($tw.utils.parseNumber(title));
 		});
+		// We return an empty array if there are no input titles
+		if(result.length === 0) {
+			return [];
+		}
 		var value = result.reduce(function(accumulator,currentValue) {
 				return fnCalc(accumulator,currentValue);
 			},initialValue);
diff --git a/editions/test/tiddlers/tests/test-prefixes-filter.js b/editions/test/tiddlers/tests/test-prefixes-filter.js
index 7b1e5b479f..68be6fe542 100644
--- a/editions/test/tiddlers/tests/test-prefixes-filter.js
+++ b/editions/test/tiddlers/tests/test-prefixes-filter.js
@@ -372,13 +372,13 @@ describe("'reduce' and 'intersection' filter prefix tests", function() {
 	it("should handle the variance operator", function() {
 		expect(parseFloat(wiki.filterTiddlers("[tag[shopping]get[price]variance[]]").join(","))).toBeCloseTo(2.92);
 		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]variance[]]").join(","))).toBeCloseTo(3.367);
-		expect(wiki.filterTiddlers(" +[variance[]]").toString()).toBe("NaN");
+		expect(wiki.filterTiddlers(" +[variance[]]").toString()).toBe("");
 	});
 
 	it("should handle the standard-deviation operator", function() {
 		expect(parseFloat(wiki.filterTiddlers("[tag[shopping]get[price]standard-deviation[]]").join(","))).toBeCloseTo(1.71);
 		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]standard-deviation[]]").join(","))).toBeCloseTo(1.835);
-		expect(wiki.filterTiddlers(" +[standard-deviation[]]").toString()).toBe("NaN");
+		expect(wiki.filterTiddlers(" +[standard-deviation[]]").toString()).toBe("");
 	});	
 
 	it("should handle the :intersection prefix", function() {