Boolean expressions in SQL Server jobs - sql-server

Question

I have inherited a SQL Server "job" that does several things. There are two "steps" and each has multiple statements one is:
UPDATE Person
SET Person.LastName = P.LastName,
Person.FirstName = P.FirstName,
Person.MiddleName = P.MiddleName,
Person.EmailAddress = P.EmailAddress,
Person.StartDate = P.StartDate,
Person.EndDate = P.EndDate
FROM OtherDB.dbo.Person Person
INNER JOIN FirstDB.dbo.Persons AS P ON P.PersonId = Person.PersonId
WHERE Person.LastName != P.LastName
OR Person.FirstName != P.FirstName
OR Person.MiddleName != P.MiddleName
OR Person.EmailAddress != P.EmailAddress
OR Person.StartDate != P.StartDate
OR Person.EndDate != P.EndDate;
It is updating "person" data from FirstDB into OtherDB. The PersonId columns are bigints and are not null. The various "date" columns are of type datetime and could be NULL. The other columns are all varchar and could be NULL.
What I have learned is that, in the where clause, if NULL appears on either or both sides of the boolean operator the result is undefined. Basically, NULL can neither equal nor not-equal NULL. It appears that the same applies to NULL and any other non-null value.
So I thought to try:
UPDATE Person
SET Person.LastName = P.LastName,
Person.FirstName = P.FirstName,
Person.MiddleName = P.MiddleName,
Person.EmailAddress = P.EmailAddress,
Person.StartDate = P.StartDate,
Person.EndDate = P.EndDate
FROM OtherDB.dbo.Person Person
INNER JOIN FirstDB.dbo.Persons AS P ON P.PersonId = Person.PersonId
WHERE ISNULL(Person.LastName, '') != ISNULL(P.LastName, '')
OR ISNULL(Person.FirstName, '') != ISNULL(P.FirstName, '')
OR ISNULL(Person.MiddleName, '') != ISNULL(P.MiddleName, '')
OR ISNULL(Person.EmailAddress, '') != ISNULL(P.EmailAddress, '')
OR ISNULL(Person.StartDate, '') != ISNULL(P.StartDate, '')
OR ISNULL(Person.EndDate, '') != ISNULL(P.EndDate, '');
This works in a regular query window but fails in the job. The error is:
An expression of non-boolean type specified in a context where a condition is expected, near 'OR'. [SQLSTATE 42000] (Error 4145). The step failed.
I am not seeing a problem. What am I missing?
Edit
As requested, for others in this situation: I edited this job by using SQL Server Management Studio. I opened a connection to my target DB then opened the "SQL Server Agent" drop-down under the connection. I opened "Jobs" and found the job i was looking for. I right-clicked on the job name and selected "Script Job As" -> "Drop and Create to" -> "New Query Window". From there I copied the relevant sections to new query windows where I modified and tested them as necessary. I then just copied and pasted the working sections back into the job window above -- COMPLETELY forgetting to double up the single quotes where necessary.

Answer 1

How did you add the step to the job? I wonder if a script you used escaped all of your double apostrophes and it is now trying to evaluate
WHERE ISNULL(Person.LastName, ') != ISNULL(P.LastName, ')
------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^
That's "valid enough" syntax. The highlighted portion is a simple string literal, not an empty string and a comparison to another expression.