Fix merging context/datasources config

internal/config/configfile.go

@@ -264,8 +264,16 @@ func (c *Config) MergeFrom(o *Config) *Config {
 	if !isZero(o.Templates) {
 		c.Templates = o.Templates
 	}
-	mergeDataSources(c.DataSources, o.DataSources)
-	mergeDataSources(c.Context, o.Context)
+	if c.DataSources == nil {
+		c.DataSources = o.DataSources
+	} else {
+		mergeDataSources(c.DataSources, o.DataSources)
+	}
+	if c.Context == nil {
+		c.Context = o.Context
+	} else {
+		mergeDataSources(c.Context, o.Context)
+	}
 	if len(o.Plugins) > 0 {
 		for k, v := range o.Plugins {
 			c.Plugins[k] = v

internal/config/configfile_test.go

@@ -329,6 +329,61 @@ func TestMergeFrom(t *testing.T) {
 	}
 
 	assert.EqualValues(t, expected, cfg.MergeFrom(other))
+
+	cfg = &Config{
+		Input:   "hello world",
+		OutMode: "644",
+	}
+	other = &Config{
+		OutputFiles: []string{"out.txt"},
+		Context: map[string]DataSource{
+			"foo": {
+				URL: mustURL("https://example.com/foo.yaml"),
+				Header: http.Header{
+					"Accept": {"application/json"},
+				},
+			},
+			"bar": {URL: mustURL("stdin:///")},
+		},
+		DataSources: map[string]DataSource{
+			"data": {
+				URL: mustURL("file:///data.json"),
+			},
+			"moredata": {
+				URL: mustURL("https://example.com/more.json"),
+				Header: http.Header{
+					"Authorization": {"Bearer abcd1234"},
+				},
+			},
+		},
+	}
+	expected = &Config{
+		Input:       "hello world",
+		OutputFiles: []string{"out.txt"},
+		Context: map[string]DataSource{
+			"foo": {
+				URL: mustURL("https://example.com/foo.yaml"),
+				Header: http.Header{
+					"Accept": {"application/json"},
+				},
+			},
+			"bar": {URL: mustURL("stdin:///")},
+		},
+		DataSources: map[string]DataSource{
+			"data": {
+				URL: mustURL("file:///data.json"),
+			},
+			"moredata": {
+				URL: mustURL("https://example.com/more.json"),
+				Header: http.Header{
+					"Authorization": {"Bearer abcd1234"},
+				},
+			},
+		},
+		OutMode: "644",
+	}
+
+	assert.EqualValues(t, expected, cfg.MergeFrom(other))
 }
 
 func TestParseDataSourceFlags(t *testing.T) {