🐛 Fix StackOverflowException converting unit for default(TQuantity)

Fixes #1118  and #1116 

- replacing the use of the nullable `_unit` field in the `TryToUnit` funtion
- added `ToUnit_FromDefaultQuantity_ReturnsQuantityWithGivenUnit` - a test for converting from `default(TQuantity)`, skipped for FuelEfficieny due to the resulting division by zero
- removed extra commas from the PressureChangeRate.json (reported as errors by the designer..)

Author: lipchev

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -985,13 +985,13 @@ double IQuantity.As(Enum unit)
         /// <returns>True if successful, otherwise false.</returns>
         private bool TryToUnit({_quantity.Name}Unit unit, out {_quantity.Name}? converted)
         {{
-            if (_unit == unit)
+            if (Unit == unit)
             {{
                 converted = this;
                 return true;
             }}
 
-            converted = (_unit, unit) switch
+            converted = (Unit, unit) switch
             {{
                 // {_quantity.Name}Unit -> BaseUnit");
 

CodeGen/Generators/UnitsNetGen/UnitTestBaseClassGenerator.cs

@@ -396,6 +396,15 @@ public void ToUnit_FromNonBaseUnit_ReturnsQuantityWithGivenUnit({_unitEnumName}
             Assert.Equal(converted.Unit, unit);
         }}
 
+        [Theory]
+        [MemberData(nameof(UnitTypes))]
+        public virtual void ToUnit_FromDefaultQuantity_ReturnsQuantityWithGivenUnit({_unitEnumName} unit)
+        {{
+            var quantity = default({_quantity.Name});
+            var converted = quantity.ToUnit(unit);
+            Assert.Equal(converted.Unit, unit);
+        }}
+
         [Fact]
         public void ConversionRoundTrip()
         {{

Common/UnitDefinitions/PressureChangeRate.json

@@ -50,11 +50,11 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "mmHg/s" ],
+          "Abbreviations": [ "mmHg/s" ]
         },
         {
           "Culture": "ru-RU",
-          "Abbreviations": [ "mmHg/с" ],
+          "Abbreviations": [ "mmHg/с" ]
         }
       ]
     },

UnitsNet.Tests/CustomCode/FuelEfficiencyTests.cs

@@ -18,6 +18,8 @@
 // Copyright 2013 Andreas Gullberg Larsen ([email protected]). Maintained at https://github.com/angularsen/UnitsNet.
 
 using System;
+using UnitsNet.Units;
+using Xunit;
 
 namespace UnitsNet.Tests.CustomCode
 {
@@ -28,5 +30,12 @@ public class FuelEfficiencyTests : FuelEfficiencyTestsBase
         protected override double LitersPer100KilometersInOneLiterPer100Kilometers => 1;
         protected override double MilesPerUkGallonInOneLiterPer100Kilometers => 282.4809363;
         protected override double MilesPerUsGallonInOneLiterPer100Kilometers => 235.2145833;
+        
+        [Theory(Skip = "Conversion from 0 km/L results in infinity")]
+        [MemberData(nameof(UnitTypes))]
+        public override void ToUnit_FromDefaultQuantity_ReturnsQuantityWithGivenUnit(FuelEfficiencyUnit unit)
+        {
+            base.ToUnit_FromDefaultQuantity_ReturnsQuantityWithGivenUnit(unit);
+        }
     }
 }