FilterType default for expectsPossibleValues now represents most common case
FilterType factory method uses a switch statement
FilterType support for 'short' and 'decimal'
No unnecessary safe navigation operators on FilterType class
Filter 'type' attribute can not be empty
Handle case where no Filter was created (invalid 'type')
FilterController updateFilter method logs problem with the specific values used
Filter possibleValues validation logs message on failure
Filters not saved in a WFS scan do not cause a 500 response code
BoundingBox FilterType matched against string explicitly
BoundingBox FilterType matches for CurvePropertyType
Tidy-up
Changes from code review
Using correct operator for null check
Merge pull request #987 from aodn/Issue_#797

Issue #797