Error converting data type varchar to numeric in standard audit trigger - triggers

Question

I have been using a standard block of TSQL for auditing of various tables for some time now. However I now have a problem when running the trigger on a new table: "Error converting data type varchar to numeric". This occurs when running the EXEC (#sql) line. I've determined that the code for #sql is:
insert Audit_AppointmentsWS
(Type,
TableName,
PK,
FieldName,
OldValue,
NewValue,
UpdateDate,
UserName)
SELECT 'U',
'AppointmentsWorkshop',
+convert(varchar(100), coalesce(i.UniqueID,d.UniqueID)),
'[JobHours]',
convert(varchar(1000),d.[JobHours]),
convert(varchar(1000),i.[JobHours]),
'20220816 12:32:43:410',
'DELLXPS\ian'
from #ins i full outer join #del d on i.UniqueID = d.UniqueID where ISNULL(i.JobHours],'') <> ISNULL(d.[JobHours],'')
I've tried deleting the trigger & the audit table and then recreating them but no joy. I've also tried copying an existing trigger and just changing the table details but I still get the same error. I'm completely stumped on this and would appreciate some feedback. Many thanks in advance!
Here is the trigger:
/****** Object: Trigger [dbo].[tr_AppointmentsWS] Script Date: 16/08/2022 12:02:10 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create TRIGGER [dbo].[tr_AppointmentsWS] ON [dbo].AppointmentsWorkshop FOR UPDATE, DELETE
AS
DECLARE #bit INT ,
#field INT ,
#maxfield INT ,
#char INT ,
#fieldname VARCHAR(128) ,
#TableName VARCHAR(128) ,
#AuditTable VARCHAR(128) ,
#PKCols VARCHAR(MAX) ,
#sql VARCHAR(2000),
#UpdateDate VARCHAR(21) ,
#UserName VARCHAR(128) ,
#Type CHAR(1) ,
#PKSelect VARCHAR(MAX)
--Changes required:
-- 1. Change the name of the trigger and the table, above
-- 2. Change #TableName to match the table to be audited
-- 3. Change the #AuditTable to the table holding the changes
SELECT #TableName = 'AppointmentsWorkshop'
SELECT #AuditTable = 'Audit_AppointmentsWS'
-- date and user
SELECT #UserName = SYSTEM_USER ,
#UpdateDate = CONVERT(VARCHAR(8), GETDATE(), 112) + ' ' + CONVERT(VARCHAR(12), GETDATE(), 114)
-- Action
IF EXISTS (SELECT * FROM inserted)
IF EXISTS (SELECT * FROM deleted)
SELECT #Type = 'U'
ELSE
SELECT #Type = 'I'
ELSE
SELECT #Type = 'D'
-- get list of columns
SELECT * INTO #ins FROM inserted
SELECT * INTO #del FROM deleted
-- Get primary key columns for full outer join
SELECT #PKCols = COALESCE(#PKCols + ' and', ' on') + ' i.' + c.COLUMN_NAME + ' = d.' + c.COLUMN_NAME
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk, INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
WHERE pk.TABLE_NAME = #TableName
AND CONSTRAINT_TYPE = 'PRIMARY KEY'
AND c.TABLE_NAME = pk.TABLE_NAME
AND c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
-- Get primary key select for insert
SELECT #PKSelect = COALESCE(#PKSelect+'+','') + '+convert(varchar(100), coalesce(i.' + COLUMN_NAME +',d.' + COLUMN_NAME + '))'
FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk, INFORMATION_SCHEMA.KEY_COLUMN_USAGE c
WHERE pk.TABLE_NAME = #TableName
AND CONSTRAINT_TYPE = 'PRIMARY KEY'
AND c.TABLE_NAME = pk.TABLE_NAME
AND c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
IF #PKCols IS NULL
BEGIN
RAISERROR('no PK on table %s', 16, -1, #TableName)
RETURN
END
SELECT #field = 0, #maxfield = MAX(COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + #Tablename),COLUMN_NAME, 'ColumnID'))
FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = #TableName
WHILE #field < #maxfield
BEGIN
SELECT #field = MIN(COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + #Tablename),COLUMN_NAME, 'ColumnID'))
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = #TableName
AND COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + #Tablename),COLUMN_NAME, 'ColumnID') > #field
SELECT #bit = (#field - 1 )% 8 + 1
SELECT #bit = POWER(2,#bit - 1)
SELECT #char = ((#field - 1) / 8) + 1
IF SUBSTRING(COLUMNS_UPDATED(),#char, 1) & #bit > 0 OR #Type IN ('I','D')
BEGIN
SELECT #fieldname = COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = #TableName
AND COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + #Tablename),COLUMN_NAME, 'ColumnID') = #field
SELECT #sql = 'insert ' + #AuditTable + '
(Type,
TableName,
PK,
FieldName,
OldValue,
NewValue,
UpdateDate,
UserName)
SELECT ''' + #Type + ''','''
+ #TableName + ''',' + #PKSelect
+ ',''[' + #fieldname + ']'''
+ ',convert(varchar(1000),d.[' + #fieldname + '])'
+ ',convert(varchar(1000),i.[' + #fieldname + '])'
+ ',''' + #UpdateDate + ''''
+ ',''' + #UserName + ''''
+ ' from #ins i full outer join #del d'
+ #PKCols
+ ' where ISNULL(i.[' + #fieldname + '],'''') <> ISNULL(d.[' + #fieldname + '],'''')' --Skip identical values and excludes NULLS vs empty strings
EXEC (#sql)
END
END

Answer 1

Well I finally figured it out. The error is being generated with columns of data type 'decimal' and it is down to the ISNULL section of the last SELECT. I've fixed it by checking for the decimal type and then using the following code (which included a zero rather than an empty sting):
+ ' where ISNULL(i.[' + #fieldname + '],''0'') <> ISNULL(d.[' + #fieldname + '],''0'')' --Skip identical values and excludes NULLS vs empty strings