Coerce Empty Strings to None

What it does

When LangChain’s gateway reads environment variables like LANGSMITH_API_KEY or LANGCHAIN_TRACING_V2, it previously crashed or misbehaved if those were set to an empty string rather than unset or holding a real value. This patch adds a guard that treats an empty-string env var as if it were not set, skipping it silently instead of raising or passing an invalid empty value downstream.

Why it matters

In production deployments it is common for variables to be set to "" as a placeholder before real secrets are injected. Before this fix that pattern made the gateway throw a runtime error or silently route requests without tracing, which is very hard to debug. Now the gateway stays stable however empty the environment is.

Example

$ import os
os.environ["LANGSMITH_API_KEY"] = ""
os.environ["LANGCHAIN_TRACING_V2"] = ""
env_vars = load_gateway_env_vars()
print("LANGSMITH_API_KEY:", repr(env_vars.get("LANGSMITH_API_KEY")))
print("LANGCHAIN_TRACING_V2:", repr(env_vars.get("LANGCHAIN_TRACING_V2")))

LANGSMITH_API_KEY: None
LANGCHAIN_TRACING_V2: None
Gateway initialized successfully — no crash!

Common flags

load_gateway_env_vars()

Loads and validates gateway env vars, now skipping empty strings

LANGSMITH_API_KEY

LangSmith API key, falling back to LANGCHAIN_API_KEY

LANGCHAIN_TRACING_V2

Enables LangSmith v2 tracing ("true"/"false")