Fixes npe when given filename ending with "." #1994

pkg/yqlib/format.go

@@ -123,9 +123,11 @@ func FormatStringFromFilename(filename string) string {
 }
 
 func FormatFromString(format string) (*Format, error) {
-	for _, printerFormat := range Formats {
+	if format != "" {
-		if printerFormat.MatchesName(format) {
+		for _, printerFormat := range Formats {
-			return printerFormat, nil
+			if printerFormat.MatchesName(format) {
+				return printerFormat, nil
+			}
 		}
 	}
 	return nil, fmt.Errorf("unknown format '%v' please use [%v]", format, GetAvailableOutputFormatString())

pkg/yqlib/format_test.go

@@ -0,0 +1,52 @@
+package yqlib
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/mikefarah/yq/v4/test"
+)
+
+type formatStringScenario struct {
+	description    string
+	input          string
+	expectedFormat *Format
+	expectedError  string
+}
+
+var formatStringScenarios = []formatStringScenario{
+	{
+		description:    "yaml",
+		input:          "yaml",
+		expectedFormat: YamlFormat,
+	},
+	{
+		description:   "Unknown format type",
+		input:         "doc",
+		expectedError: "unknown format 'doc' please use",
+	},
+	{
+		description:   "blank should error",
+		input:         "",
+		expectedError: "unknown format '' please use",
+	},
+}
+
+func TestFormatFromString(t *testing.T) {
+	for _, tt := range formatStringScenarios {
+		actualFormat, actualError := FormatFromString(tt.input)
+
+		if tt.expectedError != "" {
+			if actualError == nil {
+				t.Errorf("Expected [%v] error but found none", tt.expectedError)
+			} else {
+				test.AssertResultWithContext(t, true, strings.Contains(actualError.Error(), tt.expectedError),
+					fmt.Sprintf("Expected [%v] to contain [%v]", actualError.Error(), tt.expectedError),
+				)
+			}
+		} else {
+			test.AssertResult(t, tt.expectedFormat, actualFormat)
+		}
+	}
+}