pyln-client: add patch that fixes plugins

Without this patch, the summary and feeadjuster plugins crash on startup.

pkgs/python-packages/pyln-client/default.nix

@@ -16,5 +16,13 @@ buildPythonPackage rec {
 
   checkInputs = [ pytestCheckHook ];
 
+  # TODO-EXTERNAL:
+  # This patch is a variant (fixed relative path) of
+  # https://github.com/ElementsProject/lightning/pull/5574. This is already
+  # fixed upstream. Remove this after the next clightning release.
+  patches = [
+    ./msat-null.patch
+  ];
+
   postUnpack = "sourceRoot=$sourceRoot/contrib/${pname}";
 }

pkgs/python-packages/pyln-client/msat-null.patch

@@ -0,0 +1,16 @@
+diff --git a/pyln/client/lightning.py b/pyln/client/lightning.py
+index 38fc7563f..0013b89a3 100644
+--- a/pyln/client/lightning.py
++++ b/pyln/client/lightning.py
+@@ -455,6 +455,11 @@ class LightningRpc(UnixDomainSocketRpc):
+                     if k.endswith('msat'):
+                         if isinstance(v, list):
+                             obj[k] = [Millisatoshi(e) for e in v]
++                        # FIXME: Deprecated "listconfigs" gives two 'null' fields:
++                        #            "lease-fee-base-msat": null,
++                        #            "channel-fee-max-base-msat": null,
++                        elif v is None:
++                            obj[k] = None
+                         else:
+                             obj[k] = Millisatoshi(v)
+                     else: