Field format

Replace null values with 0 inside the RDLC report

The following statement replaces the null value with 0 else it keeps the default value
place the code inside the field expression

=iif(Parameters!emp_salary.Value like "",0,Parameters!emp_salary.Value)

Aslo you can replace a specific string with another one
For example if the string begin with “REJ” replace it with “Rejected”

=iif( left(Fields!EMP_ENROLLMENT.Value,3) like "REJ","Rejected",Fields!EMP_ENROLLMENT.Value)