Handle possible NodeList in source files when processing Middlewares // Resolve #3531

env.Object() returns a list of objects that breaks the processing of
subsequent middlewares since we only expected File nodes.

platformio/builder/tools/platformio.py

@@ -20,6 +20,7 @@ import sys
 
 from SCons import Builder, Util  # pylint: disable=import-error
 from SCons.Node import FS  # pylint: disable=import-error
+from SCons.Node import NodeList  # pylint: disable=import-error
 from SCons.Script import COMMAND_LINE_TARGETS  # pylint: disable=import-error
 from SCons.Script import AlwaysBuild  # pylint: disable=import-error
 from SCons.Script import DefaultEnvironment  # pylint: disable=import-error
@@ -285,6 +286,8 @@ def CollectBuildFiles(
     for callback, pattern in env.get("__PIO_BUILD_MIDDLEWARES", []):
         tmp = []
         for node in sources:
+            if isinstance(node, NodeList):
+                node = node[0]
             if pattern and not fnmatch.fnmatch(node.srcnode().get_path(), pattern):
                 tmp.append(node)
                 continue