The ISNULL syntax is ISNULL(check_expression, replacement_value).

According to ISNULL at docs.microsoft.com, replacement_value will be truncated if replacement_value is longer than check_expression.

Example (Microsoft SQL Server):

DECLARE @name1 VARCHAR(2) = NULL;
DECLARE @name2 VARCHAR(10) = 'Example';
DECLARE @name3 VARCHAR(2) = 'Hi';

  -- `@name2` is VARCHAR(10) and will be truncated
SELECT ISNULL(@name1, @name2);

  -- `@name3` is VARCHAR(2) as `@name1` and will not be truncated
SELECT ISNULL(@name1, @name3);