fix bug

Signed-off-by: Jack Schofield <[email protected]>

Author: jackschofield23

src/WorkflowExecuter/Common/ArtifactMapper.cs

@@ -116,9 +116,14 @@ private async Task<KeyValuePair<string, string>> ConvertVariableStringToPath(Art
                 if (string.Equals(variableLocation, "artifacts", StringComparison.InvariantCultureIgnoreCase))
                 {
                     var artifactName = variableWords[4];
-                    var outputArtifact = task.OutputArtifacts.FirstOrDefault(a => a.Key == artifactName);
+                    var outputArtifact = task.OutputArtifacts?.FirstOrDefault(a => a.Key == artifactName);
 
-                    return await VerifyExists(outputArtifact, bucketId, shouldExistYet);
+                    if (outputArtifact is null)
+                    {
+                        return default;
+                    }
+
+                    return await VerifyExists((KeyValuePair<string, string>)outputArtifact, bucketId, shouldExistYet);
                 }
             }