From 4a232c2e495677e7789a3efa4c87b04de648fce5 Mon Sep 17 00:00:00 2001
From: Willem <99329835+willem-syt@users.noreply.github.com>
Date: Mon, 23 Dec 2024 17:32:22 +0100
Subject: [PATCH] fix: output null for empty MTA (air) or MTW (water)
 temperature. (#258)

---
 hooks/MTA.js | 4 ++--
 hooks/MTW.js | 5 ++---
 test/MTA.js  | 9 +++++++++
 test/MTW.js  | 9 +++++++++
 4 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/hooks/MTA.js b/hooks/MTA.js
index 4203042d..ba17b09b 100644
--- a/hooks/MTA.js
+++ b/hooks/MTA.js
@@ -27,7 +27,7 @@ const utils = require('@signalk/nmea0183-utilities')
  *
  * Field Number:
  *   0.    Degrees
- *   1.    Unit of Measurement, Celcius
+ *   1.    Unit of Measurement, Celsius
  *   2.    Checksum
  *
  */
@@ -46,7 +46,7 @@ module.exports = function (input) {
         values: [
           {
             path: 'environment.outside.temperature',
-            value: utils.transform(utils.float(parts[0]), 'c', 'k'),
+            value: parts.length > 0 && parts[0].trim().length > 0 ? utils.transform(utils.float(parts[0]), 'c', 'k') : null,
           },
         ],
       },
diff --git a/hooks/MTW.js b/hooks/MTW.js
index 91c93e50..21f6c1f0 100644
--- a/hooks/MTW.js
+++ b/hooks/MTW.js
@@ -27,7 +27,7 @@ const utils = require('@signalk/nmea0183-utilities')
  *
  * Field Number:
  *   0.    Degrees
- *   1.    Unit of Measurement, Celcius
+ *   1.    Unit of Measurement, Celsius
  *   2.    Checksum
  *
  */
@@ -43,8 +43,7 @@ module.exports = function (input) {
         values: [
           {
             path: 'environment.water.temperature',
-            value: utils.transform(utils.float(parts[0]), 'c', 'k'),
-            //returns raw value, no transformation done
+            value: parts.length > 0 && parts[0].trim().length > 0 ? utils.transform(utils.float(parts[0]), 'c', 'k') : null,
           },
         ],
       },
diff --git a/test/MTA.js b/test/MTA.js
index fa891e97..de172038 100644
--- a/test/MTA.js
+++ b/test/MTA.js
@@ -37,4 +37,13 @@ describe('MTA', () => {
 
     should.equal(delta, null)
   })
+
+  it('Converts empty value to null', () => {
+    const delta = new Parser().parse('$RAMTA,,C*08')
+    delta.updates[0].values.length.should.equal(1)
+    delta.updates[0].values[0].path.should.equal(
+      'environment.outside.temperature'
+    )
+    chai.expect(delta.updates[0].values[0].value).to.be.null
+  })
 })
diff --git a/test/MTW.js b/test/MTW.js
index 6e9ef577..36355890 100644
--- a/test/MTW.js
+++ b/test/MTW.js
@@ -32,4 +32,13 @@ describe('MTW', () => {
     )
     delta.updates[0].values[0].value.should.be.closeTo(288.35, 0.005)
   })
+
+  it('Converts empty value to null', () => {
+    const delta = new Parser().parse('$RAMTW,,C*1E')
+    delta.updates[0].values.length.should.equal(1)
+    delta.updates[0].values[0].path.should.equal(
+      'environment.water.temperature'
+    )
+    chai.expect(delta.updates[0].values[0].value).to.be.null
+  })
 })