Do not send null or empty values (#5128)

Author: mhoeger

src/WebJobs.Script/OutOfProc/Rpc/LanguageWorkerChannel.cs

@@ -225,7 +225,11 @@ internal FunctionEnvironmentReloadRequest GetFunctionEnvironmentReloadRequest(ID
             FunctionEnvironmentReloadRequest request = new FunctionEnvironmentReloadRequest();
             foreach (DictionaryEntry entry in processEnv)
             {
-                request.EnvironmentVariables.Add(entry.Key.ToString(), entry.Value.ToString());
+                // Do not add environment variables with empty or null values (see issue #4488 for context)
+                if (!string.IsNullOrEmpty(entry.Value?.ToString()))
+                {
+                    request.EnvironmentVariables.Add(entry.Key.ToString(), entry.Value.ToString());
+                }
             }
             return request;
         }

test/WebJobs.Script.Tests/Rpc/LanguageWorkerChannelTests.cs

@@ -214,10 +214,14 @@ public async Task SendSendFunctionEnvironmentReloadRequest_ThrowsTimeout()
         [Fact]
         public void SendSendFunctionEnvironmentReloadRequest_SanitizedEnvironmentVariables()
         {
-            Environment.SetEnvironmentVariable("TestNull", null);
-            Environment.SetEnvironmentVariable("TestEmpty", string.Empty);
-            Environment.SetEnvironmentVariable("TestValid", "TestValue");
-            FunctionEnvironmentReloadRequest envReloadRequest = _workerChannel.GetFunctionEnvironmentReloadRequest(Environment.GetEnvironmentVariables());
+            var environmentVariables = new Dictionary<string, string>()
+            {
+                { "TestNull", null },
+                { "TestEmpty", string.Empty },
+                { "TestValid", "TestValue" }
+            };
+
+            FunctionEnvironmentReloadRequest envReloadRequest = _workerChannel.GetFunctionEnvironmentReloadRequest(environmentVariables);
             Assert.False(envReloadRequest.EnvironmentVariables.ContainsKey("TestNull"));
             Assert.False(envReloadRequest.EnvironmentVariables.ContainsKey("TestEmpty"));
             Assert.True(envReloadRequest.EnvironmentVariables.ContainsKey("TestValid"));