I am trying to set a property called "NumberOfLines" in a custom field
that inherits from SPFieldMultiLineText. Now, when I do the following

this.NumberOfLines = GetCustomProperty("NumberOfLines") in a method
(called Init invoked in constructor), I get "Object reference not set
to an instance of object". I made sure that I defined custom property
under PropertySchema in fldtypes*.xml file.
Please let me know if I am missing something.