4.9.0

• Added is_null and is_not_null operators (issue #494) (PR #522)
• ! Breaking change for operators is_empty and is_not_empty. Left for text type only, for other types will be auto converted to is_null/is_not_null. Changed meaning of is_empty - now it's just strict comparing with empty string. Before change meaning was similar to is_null (and export to SQL was wrong because of non-existent operator IS EMPTY). (issue #494) (PR #573)
• Fixed order of operators for field when merging operators from 2+ widgets (PR #573)
• Added last param fieldDef for functions to format operators (PR #573)
• Added jsonLogic to widget TS def (PR #572)
• Export TreeUtils (PR #597)