Geneva Exporter - Throw on TableNameMappings null value

src/OpenTelemetry.Exporter.Geneva/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+* Throw exception when `TableNameMappings` contains a `null` value.
+[322](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/322)
+
 ## 1.2.6 [2022-Apr-21]
 
 * Set GenevaMetricExporter temporality preference back to Delta.

src/OpenTelemetry.Exporter.Geneva/GenevaExporterOptions.cs

@@ -27,11 +27,36 @@ public class GenevaExporterOptions
         [Schema.V40.PartA.Ver] = "4.0",
     };
 
+    private IReadOnlyDictionary<string, string> _tableNameMappings;
+
     public string ConnectionString { get; set; }
 
     public IEnumerable<string> CustomFields { get; set; }
 
-    public IReadOnlyDictionary<string, string> TableNameMappings { get; set; }
+    public IReadOnlyDictionary<string, string> TableNameMappings
+    {
+        get => this._tableNameMappings;
+        set
+        {
+            Guard.ThrowIfNull(value);
+
+            foreach (var entry in value)
+            {
+                if (entry.Value is null)
+                {
+                    throw new ArgumentNullException(entry.Key, $"{nameof(this.TableNameMappings)} must not contain null values.");
+                }
+            }
+
+            var copy = new Dictionary<string, string>(value.Count);
+            foreach (var entry in value)
+            {
+                copy[entry.Key] = entry.Value; // shallow copy
+            }
+
+            this._tableNameMappings = copy;
+        }
+    }
 
     public IReadOnlyDictionary<string, object> PrepopulatedFields
     {

src/OpenTelemetry.Exporter.Geneva/OpenTelemetry.Exporter.Geneva.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

test/OpenTelemetry.Exporter.Geneva.Tests/GenevaLogExporterTests.cs

@@ -62,6 +62,26 @@ public void SpecialChractersInTableNameMappings()
                     TableNameMappings = new Dictionary<string, string> { ["*"] = "\u0418" },
                 });
             });
+
+            // Throw on null value - include key in exception message
+            var ex = Assert.Throws<ArgumentNullException>(() =>
+            {
+                new GenevaExporterOptions
+                {
+                    TableNameMappings = new Dictionary<string, string> { ["TestCategory"] = null },
+                };
+            });
+            Assert.Contains("TableNameMappings must not contain null values.", ex.Message);
+            Assert.Equal("TestCategory", ex.ParamName);
+
+            // Throw when TableNameMappings is null
+            Assert.Throws<ArgumentNullException>(() =>
+            {
+                new GenevaExporterOptions
+                {
+                    TableNameMappings = null,
+                };
+            });
         }
 
         [Theory]