diff --git a/libs/langchain/langchain/schema/runnable/config.py b/libs/langchain/langchain/schema/runnable/config.py
index 44f99b6510f..1b720fb5b6e 100644
--- a/libs/langchain/langchain/schema/runnable/config.py
+++ b/libs/langchain/langchain/schema/runnable/config.py
@@ -159,17 +159,25 @@ def patch_config(
 
 def merge_configs(*configs: Optional[RunnableConfig]) -> RunnableConfig:
     base: RunnableConfig = {}
+    # Even though the keys aren't literals this is correct
+    # because both dicts are same type
     for config in (c for c in configs if c is not None):
         for key in config:
             if key == "metadata":
-                base[key] = {**base.get(key, {}), **config[key]}  # type: ignore
+                base[key] = {  # type: ignore
+                    **base.get(key, {}),  # type: ignore
+                    **(config.get(key) or {}),  # type: ignore
+                }
             elif key == "tags":
-                base[key] = list(set(base.get(key, []) + config[key]))  # type: ignore
+                base[key] = list(  # type: ignore
+                    set(base.get(key, []) + (config.get(key) or [])),  # type: ignore
+                )
             elif key == "configurable":
-                base[key] = {**base.get(key, {}), **config[key]}  # type: ignore
+                base[key] = {  # type: ignore
+                    **base.get(key, {}),  # type: ignore
+                    **(config.get(key) or {}),  # type: ignore
+                }
             else:
-                # Even though the keys aren't literals this is correct
-                # because both dicts are same type
                 base[key] = config[key] or base.get(key)  # type: ignore
     return base