Fix username-only creds

src/main/groovy/org/ajoberstar/grgit/Credentials.groovy

@@ -15,14 +15,26 @@
  */
 package org.ajoberstar.grgit
 
-import groovy.transform.Immutable
+import groovy.transform.Canonical
 
 /**
  * Credentials to use for remote operations.
  * @since 0.2.0
  */
-@Immutable
+@Canonical
 class Credentials {
-  String username
-  String password
+  final String username
+  final String password
+
+  String getUsername() {
+    return username ?: ''
+  }
+
+  String getPassword() {
+    return password ?: ''
+  }
+
+  boolean isPopulated() {
+    return username != null
+  }
 }

src/main/groovy/org/ajoberstar/grgit/auth/AuthConfig.groovy

@@ -156,11 +156,7 @@ class AuthConfig {
     if (allows(Option.HARDCODED)) {
       String username = props[USERNAME_OPTION] ?: env[USERNAME_ENV_VAR]
       String password = props[PASSWORD_OPTION] ?: env[PASSWORD_ENV_VAR]
-      if (username) {
-        return new Credentials(username, password)
-      } else {
-        return null
-      }
+      return new Credentials(username, password)
     } else {
       return null
     }

src/main/groovy/org/ajoberstar/grgit/auth/TransportOpUtil.groovy

@@ -52,10 +52,10 @@ final class TransportOpUtil {
 
   private static CredentialsProvider determineCredentialsProvider(AuthConfig config, Credentials creds) {
     Credentials systemCreds = config.hardcodedCreds
-    if (config.allows(AuthConfig.Option.HARDCODED) && creds?.username) {
+    if (config.allows(AuthConfig.Option.HARDCODED) && creds?.populated) {
       logger.info('using hardcoded credentials provided programmatically')
       return new UsernamePasswordCredentialsProvider(creds.username, creds.password)
-    } else if (config.allows(AuthConfig.Option.HARDCODED) && systemCreds) {
+    } else if (config.allows(AuthConfig.Option.HARDCODED) && systemCreds?.populated) {
       logger.info('using hardcoded credentials from system properties')
       return new UsernamePasswordCredentialsProvider(systemCreds.username, systemCreds.password)
     } else if (config.allows(AuthConfig.Option.INTERACTIVE) && !GraphicsEnvironment.isHeadless()) {

src/test/groovy/org/ajoberstar/grgit/auth/AuthConfigSpec.groovy

@@ -67,9 +67,9 @@ class AuthConfigSpec extends Specification {
     AuthConfig.fromMap(props).getHardcodedCreds() == new Credentials('myuser', null)
   }
 
-  def 'getHardcodedCreds returns null if username is not set'() {
+  def 'getHardcodedCreds are not populated if username is not set'() {
     expect:
-    AuthConfig.fromMap([:]).getHardcodedCreds() == null
+    !AuthConfig.fromMap([:]).getHardcodedCreds().isPopulated()
   }
 
   def 'getSessionConfig returns empty map if nothing specified'() {

src/test/groovy/org/ajoberstar/grgit/auth/LinuxAuthenticationSpec.groovy

@@ -34,6 +34,7 @@ class LinuxAuthenticationSpec extends Specification {
   private static final String HTTPS_URI = 'https://github.com/ajoberstar/grgit-test.git'
 
   static Credentials hardcodedCreds
+  static Credentials partialCreds
 
   @Rule TemporaryFolder tempDir = new TemporaryFolder()
 
@@ -45,6 +46,7 @@ class LinuxAuthenticationSpec extends Specification {
     def username = System.properties['org.ajoberstar.grgit.test.username']
     def password = System.properties['org.ajoberstar.grgit.test.password']
     hardcodedCreds = new Credentials(username, password)
+    partialCreds = new Credentials(password, null)
     assert hardcodedCreds.username && hardcodedCreds.password
   }
 
@@ -61,7 +63,7 @@ class LinuxAuthenticationSpec extends Specification {
     System.properties[AuthConfig.FORCE_OPTION] = method
     assert System.properties[AuthConfig.USERNAME_OPTION] == null, 'Username should not already be set.'
     assert System.properties[AuthConfig.PASSWORD_OPTION] == null, 'Password should not already be set.'
-    ready(ssh, creds)
+    ready(ssh)
     if (!creds) {
       System.properties[AuthConfig.USERNAME_OPTION] = hardcodedCreds.username
       System.properties[AuthConfig.PASSWORD_OPTION] = hardcodedCreds.password
@@ -72,18 +74,18 @@ class LinuxAuthenticationSpec extends Specification {
     then:
     grgit.branch.status(branch: 'master').aheadCount == 0
     where:
-    method		| ssh   | creds
+    method		    | ssh   | creds
     'hardcoded'   | false | hardcodedCreds
-    'hardcoded'   | false | null
+    'hardcoded'   | false | partialCreds
     'interactive' | false | null
     'interactive' | true  | null
-    'sshagent'	| true  | null
+    'sshagent'	  | true  | null
   }
 
-  private void ready(boolean ssh, Credentials credentials = null) {
+  private void ready(boolean ssh) {
     File repoDir = tempDir.newFolder('repo')
     String uri = ssh ? SSH_URI : HTTPS_URI
-    grgit = Grgit.clone(uri: uri, dir: repoDir, credentials: credentials)
+    grgit = Grgit.clone(uri: uri, dir: repoDir)
     grgit.repository.jgit.repo.config.with {
       setString('user', null, 'name', person.name)
       setString('user', null, 'email', person.email)

src/test/groovy/org/ajoberstar/grgit/auth/WindowsAuthenticationSpec.groovy

@@ -46,7 +46,7 @@ class WindowsAuthenticationSpec extends Specification {
     def username = System.properties['org.ajoberstar.grgit.test.username']
     def password = System.properties['org.ajoberstar.grgit.test.password']
     hardcodedCreds = new Credentials(username, password)
-    partialCreds = new Credentials(username, null)
+    partialCreds = new Credentials(password, null)
     assert hardcodedCreds.username && hardcodedCreds.password
   }
 
@@ -63,7 +63,7 @@ class WindowsAuthenticationSpec extends Specification {
     assert System.properties[AuthConfig.USERNAME_OPTION] == null, 'Username should not already be set.'
     assert System.properties[AuthConfig.PASSWORD_OPTION] == null, 'Password should not already be set.'
     System.properties[AuthConfig.FORCE_OPTION] = method
-    ready(ssh, creds)
+    ready(ssh)
     if (!creds) {
       System.properties[AuthConfig.USERNAME_OPTION] = hardcodedCreds.username
       System.properties[AuthConfig.PASSWORD_OPTION] = hardcodedCreds.password
@@ -74,20 +74,20 @@ class WindowsAuthenticationSpec extends Specification {
     then:
     grgit.branch.status(branch: 'master').aheadCount == 0
     where:
-    method		| ssh   | creds
+    method		    | ssh   | creds
     'hardcoded'   | false | hardcodedCreds
     'hardcoded'   | false | partialCreds
     'hardcoded'   | false | null
     'interactive' | false | null
     'interactive' | true  | null
-    'sshagent'	| true  | null
-    'pageant'	 | true  | null
+    'sshagent'	  | true  | null
+    'pageant'	    | true  | null
   }
 
-  private void ready(boolean ssh, Credentials credentials = null) {
+  private void ready(boolean ssh) {
     File repoDir = tempDir.newFolder('repo')
     String uri = ssh ? SSH_URI : HTTPS_URI
-    grgit = Grgit.clone(uri: uri, dir: repoDir, credentials: credentials)
+    grgit = Grgit.clone(uri: uri, dir: repoDir)
     grgit.repository.jgit.repo.config.with {
       setString('user', null, 'name', person.name)
       setString('user', null, 'email', person.email)