COBCH1602 Indexer must have at least one parameter

You must specify at least one parameter in the Procedure Division header:

class-id myClass1.
indexer-id string.
procedure division. *> this is incorrect - no parameter specified
    getter.
    set property-value to "abc"
end indexer.
end class.

class-id myClass2.
01 myField string value "abc".
indexer-id string.
procedure division using value myParam as binary-long. *> this is correct
    getter.
    set property-value to a
end indexer.
end class.