ReportStudio/WorkspaceAdv ReportLayout expression to support coalesce function to handle NULL string concatenation problems

FM/ReportStudio/WorkspaceAdv supports COALESCE function to handle NULL string values. This is useful when an output string is concatenation of several items and some of the items could be NULL. In most cases we want to handle NULL string values as empty values, so that result of string concatenation shows other items.

In query dataItem level this can be workarounded with coalesce function, but LayoutCalculation and Report function list doesn't support ifnull or coalesce function. Consider following header function in as reportLayout expression:
ParamDisplayValue('month') + ' / ' + ParamDisplayValue('customer') + ' / ' + ParamDisplayValue('ordermethod')

What about if all prompts are optional? The whole expression would show nothing (null string) if even one prompt value is missing. Sure we can workaround this by writing something like this:
if ParamDisplayValue('promptName') is null then ('') else (ParamDisplayValue('promptName'))

However, this is tedious work if the same expression tries to concatenate several string items. Another alternative is to use different LayoutExpression report objects in a report, but sometimes we would like to use just one LayoutExperssion object and output the whole result as a result string concatenation.

Following syntax would be a lot easier to write and maintain than nested if-then-else or case-when expression logic:

coalesce(ParamDisplayValue('month'), '') + ' / ' + coalesce(ParamDisplayValue('customer'), '') + ' / ' + coalesce(ParamDisplayValue('ordermethod'), '(no order method specified)')