Update configuration to use omitempty annotation (#13)

godelplugin/integration_test/integration_test.go

@@ -236,6 +236,27 @@ custom-headers:
     // Subproject license.
   paths:
   - subprojectDir
+`,
+				},
+			},
+			{
+				Name: "legacy config is upgraded and empty fields are omitted",
+				ConfigFiles: map[string]string{
+					"godel/config/license.yml": `
+header: |
+  // Copyright 2016 Palantir Technologies, Inc.
+  //
+  // License content.
+`,
+				},
+				Legacy: true,
+				WantOutput: `Upgraded configuration for license-plugin.yml
+`,
+				WantFiles: map[string]string{
+					"godel/config/license-plugin.yml": `header: |
+  // Copyright 2016 Palantir Technologies, Inc.
+  //
+  // License content.
 `,
 				},
 			},

golicense/config/internal/v0/config.go

@@ -14,30 +14,30 @@ type ProjectConfig struct {
 	// Header is the expected license header. All applicable files are expected to start with this header followed
 	// by a newline. Any occurrences of the string {{YEAR}} is treated specially: when generating a license, the current
 	// year will be substituted for it, and when verifying a license, any 4-digit string will be considered a match.
-	Header string `yaml:"header"`
+	Header string `yaml:"header,omitempty"`
 
 	// CustomHeaders specifies the custom header parameters. Custom header parameters can be used to specify that
 	// certain directories or files in the project should use a header that is different from "Header".
-	CustomHeaders []CustomHeaderConfig `yaml:"custom-headers"`
+	CustomHeaders []CustomHeaderConfig `yaml:"custom-headers,omitempty"`
 
 	// Exclude matches the files and directories that should be excluded from consideration for verifying or applying
 	// licenses.
-	Exclude matcher.NamesPathsCfg `yaml:"exclude"`
+	Exclude matcher.NamesPathsCfg `yaml:"exclude,omitempty"`
 }
 
 type CustomHeaderConfig struct {
 	// Name is the identifier used to identify this custom license parameter. Must be unique.
-	Name string `yaml:"name"`
+	Name string `yaml:"name,omitempty"`
 
 	// Header is the expected license header. All applicable files are expected to start with this header followed
 	// by a newline. Any occurrences of the string {{YEAR}} is treated specially: when generating a license, the current
 	// year will be substituted for it, and when verifying a license, any 4-digit string will be considered a match.
-	Header string `yaml:"header"`
+	Header string `yaml:"header,omitempty"`
 
 	// Paths specifies the paths for which this custom license is applicable. If multiple custom parameters match a
 	// file or directory, the parameter with the longest path match is used. If multiple custom parameters match a
 	// file or directory exactly (match length is equal), it is treated as an error.
-	Paths []string `yaml:"paths"`
+	Paths []string `yaml:"paths,omitempty"`
 }
 
 func UpgradeConfig(cfgBytes []byte) ([]byte, error) {