From ab891c4fbdcd42f4cedb11a704d0b3467c8f3a4b Mon Sep 17 00:00:00 2001
From: oyeong011 <oyeong011@gmail.com>
Date: Tue, 8 Sep 2026 11:48:59 +0900
Subject: [PATCH] Reject blank float arguments instead of silently using zero

The float converter passes blank strings into Number(), which returns zero. Reject empty/whitespace-only strings while preserving surrounding whitespace on valid numeric input.

Confidence: high
Scope-risk: narrow
Tested: Regression red/green, full test suite, exported API QA
---
 lib/argparse.js       |  2 +-
 test/test_argparse.js | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/lib/argparse.js b/lib/argparse.js
index 87b2f31..1613933 100644
--- a/lib/argparse.js
+++ b/lib/argparse.js
@@ -2715,7 +2715,7 @@ const ArgumentParser = _callable(class ArgumentParser extends _AttributeHolder(_
         })
         this.register('type', 'float', function (x) {
             const result = _string_to_number(x)
-            if (isNaN(result)) {
+            if (isNaN(result) || (typeof x === 'string' && !x.trim())) {
                 throw new TypeError(sub('could not convert string to float: %r', x))
             }
             return result
diff --git a/test/test_argparse.js b/test/test_argparse.js
index 82127bd..0ceb6fb 100644
--- a/test/test_argparse.js
+++ b/test/test_argparse.js
@@ -7961,3 +7961,16 @@ VV VV VV
         assert(!demo_parser.format_help().includes('\x1b['))
     }
 }).run()
+
+describe('blank float arguments', () => {
+    it('rejects empty and whitespace-only values', () => {
+        const parser = new argparse.ArgumentParser({ exit_on_error: false })
+        parser.add_argument('--float', { type: 'float' })
+        for (const value of ['', '   ', '\t\n']) {
+            assert.throws(() => parser.parse_args(['--float', value]), argparse.ArgumentError)
+        }
+        for (const value of ['0', ' 0 ', '\t1.5\n']) {
+            assert.strictEqual(parser.parse_args(['--float', value]).float, Number(value))
+        }
+    })
+})