Return false when dotenv contains only valueless declarations

src/dotenv/main.py

@@ -102,7 +102,7 @@ def set_as_environment_variables(self) -> bool:
         """
         Load the current dotenv as system environment variable.
         """
-        if not self.dict():
+        if not any(value is not None for value in self.dict().values()):
             return False
 
         for k, v in self.dict().items():

tests/test_load_result.py

@@ -0,0 +1,48 @@
+import io
+import os
+from unittest import mock
+
+import pytest
+
+from dotenv import dotenv_values, load_dotenv
+
+
+@pytest.mark.parametrize("override", [False, True])
+@pytest.mark.parametrize("source", ["file", "stream"])
+@pytest.mark.parametrize("existing", [False, True])
+@pytest.mark.parametrize(
+    "content", ["DOTENV_TEST_KEY", "# comment\nDOTENV_TEST_KEY\nOTHER_KEY\n"]
+)
+def test_load_dotenv_without_values_returns_false(
+    tmp_path, override, source, existing, content
+):
+    environ = {"DOTENV_TEST_KEY": "existing"} if existing else {}
+    with mock.patch.dict(os.environ, environ, clear=True):
+        if source == "file":
+            path = tmp_path / ".env"
+            path.write_text(content)
+            result = load_dotenv(path, override=override)
+        else:
+            result = load_dotenv(stream=io.StringIO(content), override=override)
+
+        assert result is False
+        assert os.environ == environ
+
+    assert dotenv_values(stream=io.StringIO(content))["DOTENV_TEST_KEY"] is None
+
+
+@pytest.mark.parametrize("override", [False, True])
+@pytest.mark.parametrize(
+    "content",
+    [
+        "DOTENV_TEST_KEY=",
+        "BARE_KEY\nDOTENV_TEST_KEY=",
+        "DOTENV_TEST_KEY=value\nBARE_KEY",
+    ],
+)
+def test_load_dotenv_with_values_returns_true(override, content):
+    with mock.patch.dict(os.environ, {}, clear=True):
+        result = load_dotenv(stream=io.StringIO(content), override=override)
+
+        assert result is True
+        assert os.environ == {"DOTENV_TEST_KEY": "value" if "=value" in content else ""}