From 5ce19dd99ae5d206fc5ac807289fe474259256bc Mon Sep 17 00:00:00 2001
From: Truls <20932917+truls-p@users.noreply.github.com>
Date: Wed, 24 Jan 2024 16:09:13 +0000
Subject: [PATCH] Change metadata_vars `if not` to `if ... is None` (#37)

Both None and {} evaluates to True when using if not metadata_vars. This caused us to loop over the environment variables unnecessarily. This provides a significant performance increase for large projects.
---
 .changes/unreleased/Under the Hood-20240123-194242.yaml | 6 ++++++
 dbt_common/events/functions.py                          | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 .changes/unreleased/Under the Hood-20240123-194242.yaml

diff --git a/.changes/unreleased/Under the Hood-20240123-194242.yaml b/.changes/unreleased/Under the Hood-20240123-194242.yaml
new file mode 100644
index 00000000..a0cb7431
--- /dev/null
+++ b/.changes/unreleased/Under the Hood-20240123-194242.yaml	
@@ -0,0 +1,6 @@
+kind: Under the Hood
+body: Change metadata_vars \`if not\` to \`if ... is None\`
+time: 2024-01-23T19:42:42.95727089Z
+custom:
+  Author: truls-p
+  Issue: "6073"
diff --git a/dbt_common/events/functions.py b/dbt_common/events/functions.py
index 60ef4d27..fde2219b 100644
--- a/dbt_common/events/functions.py
+++ b/dbt_common/events/functions.py
@@ -138,7 +138,7 @@ def fire_event(e: BaseEvent, level: Optional[EventLevel] = None) -> None:
 
 def get_metadata_vars() -> Dict[str, str]:
     global metadata_vars
-    if not metadata_vars:
+    if metadata_vars is None:
         metadata_vars = {
             k[len(_METADATA_ENV_PREFIX) :]: v for k, v in os.environ.items() if k.startswith(_METADATA_ENV_PREFIX)
         }