feat: support filtering out empty values (#50)

Author: drewlanenga

expr/builtins/builtins_test.go

@@ -275,6 +275,8 @@ var builtinTests = []testBuiltins{
 	{`filter(split("apples,oranges",","),"ora%")`, value.NewStringsValue([]string{"apples"})},
 	{`filter(split("apples,oranges",","),["ora%","ban*"])`, value.NewStringsValue([]string{"apples"})},
 	{`filter(split("apples,oranges",","), ["ora*","notmatch","stuff"] )`, value.NewStringsValue([]string{"apples"})},
+	{`filter(split("apples,oranges,",","), [""] )`, value.NewStringsValue([]string{"apples", "oranges"})},
+	{`filter("apples","")`, value.NewStringValue("apples")},
 	{`filter("apples","ban*")`, value.NewStringValue("apples")},
 	{`filter("apples","ban")`, value.NewStringValue("apples")},
 	{`filter("apples","app*")`, value.NilValueVal},

expr/builtins/filter.go

@@ -107,6 +107,11 @@ func FilterEval(ctx expr.EvalContext, vals []value.Value) (value.Value, bool) {
 						filteredOut = true
 						break
 					}
+				} else if filter == "" {
+					if rowKey == "" && v != nil {
+						filteredOut = true
+						break
+					}
 				} else {
 					if strings.HasPrefix(rowKey, filter) && v != nil {
 						filteredOut = true
@@ -132,6 +137,11 @@ func FilterEval(ctx expr.EvalContext, vals []value.Value) (value.Value, bool) {
 					anyMatches = true
 					break
 				}
+			} else if filter == "" {
+				if val.Val() == "" {
+					anyMatches = true
+					break
+				}
 			} else {
 				if strings.HasPrefix(val.Val(), filter) {
 					anyMatches = true
@@ -157,6 +167,11 @@ func FilterEval(ctx expr.EvalContext, vals []value.Value) (value.Value, bool) {
 						filteredOut = true
 						break
 					}
+				} else if filter == "" {
+					if sv == "" {
+						filteredOut = true
+						break
+					}
 				} else {
 					if strings.HasPrefix(sv, filter) && sv != "" {
 						filteredOut = true