test(helpers): add tests for handling empty and undefined string variables in templates

- Introduced new test cases to verify the behavior of the `processValue` function when dealing with empty string variables and undefined variables.
- Ensured that empty strings are correctly replaced and undefined variables remain unchanged in the output.

packages/server/src/templates/processors.ts

@@ -170,12 +170,12 @@ export function processValue(
 		}
 
 		// If not a utility function, try to get from variables
-		return variables[varName] || match;
+		return varName in variables ? (variables[varName] ?? match) : match;
 	});
 
 	// Then replace any remaining ${var} with their values from variables
 	processedValue = processedValue.replace(/\${([^}]+)}/g, (match, varName) => {
-		return variables[varName] || match;
+		return varName in variables ? (variables[varName] ?? match) : match;
 	});
 
 	return processedValue;