From b88ee7a927e825250adf387021df077309a14ea5 Mon Sep 17 00:00:00 2001
From: Yogthos <yogthos@gmail.com>
Date: Sat, 5 Sep 2026 23:57:36 -0400
Subject: [PATCH] Give RT/iter the empty input list
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latest/run and sample/run both open with (.iterator (seq fs)), and in both
`fs` can be empty: a zero-input (m/latest f) has no flows at all, and
(m/sample f sampler) splits its varargs so the continuous inputs are (). An
empty seq is nil, and a method call on nil is a NullPointerException.

It only ever ran because jolt through 0.8.1 answered (.iterator nil) with an
empty iterator instead of refusing it; 0.8.2 refuses it as the JVM always has,
which is what surfaced this as #4. RT/iter is what clojure.core's own walkers
use for this and takes nil on both hosts.

The sample half was unreported and uncovered — a sampler-only sample is the
single most ordinary shape of the operator. It has a row now, and it fails
without the fix.

Pin moved to 0.8.2 with the fix, per the cutover convention in ci.yml.

Closes #4.

Claude-Session: https://claude.ai/code/session_019tGgRzPx3vtr5siPkKjjLE
---
 .github/workflows/ci.yml            |  2 +-
 src/ebb/impl/latest.clj             |  9 ++++++++-
 src/ebb/impl/sample.clj             |  5 ++++-
 test/ebb/missionary_issues_test.clj | 10 ++++++++++
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d13618d..ea1ccfc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,7 +28,7 @@ on:
         default: ""
 
 env:
-  JOLT_VERSION: ${{ inputs.jolt-version || '0.8.1' }}
+  JOLT_VERSION: ${{ inputs.jolt-version || '0.8.2' }}
 
 jobs:
   test:
diff --git a/src/ebb/impl/latest.clj b/src/ebb/impl/latest.clj
index 9d0ece3..741760e 100644
--- a/src/ebb/impl/latest.clj
+++ b/src/ebb/impl/latest.clj
@@ -180,8 +180,15 @@
              (step ps i))))
     (or (= p (.-pending ps)) (terminated ps i))))
 
+;; RT/iter, not (.iterator (seq fs)): `fs` is a rest arg, so a zero-input
+;; (m/latest f) -- issue #126, a well defined continuous flow whose state is
+;; always (f) -- hands this nil, and a method call on nil is a
+;; NullPointerException. It ran only because jolt through 0.8.1 answered
+;; (.iterator nil) with an empty iterator instead of refusing it
+;; (jolt-lang/jolt#867); 0.8.2 refuses it as the JVM always has. RT/iter is what
+;; clojure.core's own walkers use for exactly this and takes nil on both hosts.
 (defn run [c fs s d]
-  (let [it (.iterator (seq fs))
+  (let [it (clojure.lang.RT/iter fs)
         arity (count fs)
         ;; `step` starts NIL, as Latest.java's does. It is what says "this flow
         ;; has no value yet": `transfer` reports Uninitialized on it, and
diff --git a/src/ebb/impl/sample.clj b/src/ebb/impl/sample.clj
index 53bf035..c84fbea 100644
--- a/src/ebb/impl/sample.clj
+++ b/src/ebb/impl/sample.clj
@@ -212,8 +212,11 @@
     (if (nil? (.-notifier ps))
       (throw x) x)))
 
+;; RT/iter for the same reason latest/run uses it: `fs` here is (rest flows),
+;; so (m/sample f sampler) with no continuous inputs -- the single-flow sample,
+;; which nothing in the suite covered -- hands this an empty seq's nil.
 (defn run [c f fs n t]
-  (let [it (.iterator (seq fs))
+  (let [it (clojure.lang.RT/iter fs)
         arity (inc (count fs))
         args (object-array arity)
         owed (int-array arity)
diff --git a/test/ebb/missionary_issues_test.clj b/test/ebb/missionary_issues_test.clj
index 8d48fad..ab6bf64 100644
--- a/test/ebb/missionary_issues_test.clj
+++ b/test/ebb/missionary_issues_test.clj
@@ -45,6 +45,16 @@
   (t/is (= [:ok [:nullary]]
           (settle (m/reduce conj [] (m/latest (fn [] :nullary)))))))
 
+(t/deftest sample-supports-a-sampler-only
+  ;; Not an upstream issue: ebb's own. `sample` splits its varargs into the
+  ;; sampler and the continuous inputs, so (m/sample f sampler) hands the impl
+  ;; an EMPTY input list -- the same nil target the zero-input latest above
+  ;; hands it, and the same NullPointerException. Nothing covered the shape,
+  ;; so it went unreported while the latest case was being filed. The result is
+  ;; (f) per sampled value, as it is with any other input count.
+  (t/is (= [:ok [[1] [2] [3]]]
+          (settle (m/reduce conj [] (m/sample vector (m/seed [1 2 3])))))))
+
 (t/deftest signal-reports-an-uninitialised-flow-125
   ;; #125: (m/signal (m/ap (m/? m/never))) leaked internal state and reported
   ;; nothing. It must fail instead.