Make the config.keygen optional in the configuration file

card-functionality/src/cards.rs

@@ -26,7 +26,7 @@ pub struct Card {
 
 #[derive(Clone, Debug, Deserialize)]
 pub struct Config {
-    pub keygen: Vec<String>,
+    pub keygen: Option<Vec<String>>,
 }
 
 /// An "opened" card, via one particular backend, with test-metadata

card-functionality/src/keygen.rs

@@ -40,7 +40,11 @@ fn main() -> Result<()> {
 
         let algos = {
             let config = card.get_config();
-            config.keygen.clone()
+            if let Some(keygen) = &config.keygen {
+                keygen.clone()
+            } else {
+                vec![]
+            }
         };
 
         for algo in algos {