Use zero for undefined fields in where expressions

This commit fixes an issue where expressions were
silently failing when encountering undefined fields.
Instead they should be treating the undefined field like
the number zero. This is required to stay compatible with
how Tile38 handles zeros.
https://tile38.com/commands/intersects/#fields

Fixes #754

internal/server/expr.go

@@ -91,6 +91,7 @@ func newExprPool(s *Server) *exprPool {
 						return resultToValue(r), nil
 					}
 				}
+				return expr.Number(0), nil
 			} else {
 				switch v := info.Value.Value().(type) {
 				case gjson.Result:
@@ -102,8 +103,8 @@ func newExprPool(s *Server) *exprPool {
 						return expr.Function("match"), nil
 					}
 				}
+				return expr.Undefined, nil
 			}
-			return expr.Undefined, nil
 		},
 		// call
 		func(info expr.CallInfo, ctx *expr.Context) (expr.Value, error) {

tests/keys_test.go

@@ -600,6 +600,17 @@ func keys_FIELDS_test(mc *mockServer) error {
 		Do("SCAN", "fleet", "WHERE", "props.speed > 53", "IDS").JSON().Str(`{"ok":true,"ids":[],"count":0,"cursor":0}`),
 		Do("SCAN", "fleet", "WHERE", "Props.speed > 53", "IDS").JSON().Str(`{"ok":true,"ids":[],"count":0,"cursor":0}`),
 		Do("SCAN", "fleet", "WHERE", "Props.Speed > 53", "IDS").JSON().Str(`{"ok":true,"ids":[],"count":0,"cursor":0}`),
+
+		Do("DROP", "fleet").JSON().OK(),
+		Do("SET", "fleet", "1", "field", "teamId", "1", "field", "optionalId", "999", "point", "0", "0").JSON().OK(),
+		Do("SET", "fleet", "2", "field", "teamId", "1", "point", "0", "0").JSON().OK(),
+		Do("SCAN", "fleet", "COUNT").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
+		Do("SCAN", "fleet", "WHEREIN", "teamId", "1", "1", "COUNT").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
+
+		Do("SCAN", "fleet", "WHEREIN", "teamId", "1", "1", "WHERE", "!optionalId || optionalId == 999", "count").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
+		Do("SCAN", "fleet", "WHEREIN", "teamId", "1", "1", "WHERE", "!!!optionalId || optionalId == 999", "count").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
+		Do("SCAN", "fleet", "WHEREIN", "teamId", "1", "1", "WHERE", "optionalId == 0 || optionalId == 999", "count").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
+		Do("SCAN", "fleet", "WHEREIN", "teamId", "1", "1", "WHERE", "1 == 1 || optionalId == 999", "count").JSON().Str(`{"ok":true,"count":2,"cursor":0}`),
 	)
 }