We use the fields area of the If Null step and say that if the incoming Date (Timestamp) is null, it should be replaced by value 1900-01-01 with conversion mask (Date) yyyy-MM-dd.
The error we get is: Error in step: Unable to verify if [CREATEDAT String] is null or not because of an error: java.lang.ClassCastException: java.util.Date cannot be cast to java.lang.String
The error happens in line 2825 of file /src-core/org/pentaho/di/core/row/ValueMeta.java. The program thinks that what we enter is a String. Probably because of the lines 74-76 in /src/org/pentaho/di/trans/steps/ifnull/IfNull.java which set the type for each row to String.
for a sample transformation