fix: tx-spammer extra args (#394)

src/transaction_spammer/transaction_spammer.star

@@ -20,12 +20,17 @@ def get_config(prefunded_addresses, el_uri, tx_spammer_extra_args, electra_fork_
         tx_spammer_image = "ethpandaops/tx-fuzz:kaustinen-281adbc"
     else:
         tx_spammer_image = "ethpandaops/tx-fuzz:master"
-    return ServiceConfig(
-        image=tx_spammer_image,
-        cmd=[
+
+    cmd = [
         "spam",
         "--rpc={}".format(el_uri),
         "--sk={0}".format(prefunded_addresses[3].private_key),
-            "{0}".format(" ".join(tx_spammer_extra_args)),
-        ],
+    ]
+
+    if len(tx_spammer_extra_args) > 0:
+        cmd.extend([param for param in tx_spammer_extra_args])
+
+    return ServiceConfig(
+        image=tx_spammer_image,
+        cmd=cmd,
     )