Fix nullable qualifier, and build

Author: Tim Baverstock

README.md

@@ -24,6 +24,10 @@ Read more about the App Bundle format and Bundletool's usage at
 Documentation of bundletool commands can be found at:
 https://developer.android.com/studio/command-line/bundletool
 
+## Build
+
+Build with: ./gradlew executableJar
+
 ## Releases
 
 Latest release: [0.10.1](https://github.com/google/bundletool/releases)

gradle/wrapper/gradle-wrapper.properties

@@ -1,4 +1,4 @@
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.0-bin.zip
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStorePath=wrapper/dists

src/main/java/com/android/tools/build/bundletool/model/version/Version.java

@@ -71,12 +71,13 @@ public static Version of(String version) {
           .build();
     }
 
+    String nullableQualifier = matcher.group("qualifier");
     return Version.builder()
         .setFullVersion(version)
         .setMajorVersion(Integer.parseInt(matcher.group("major")))
         .setMinorVersion(Integer.parseInt(matcher.group("minor")))
         .setRevisionVersion(Integer.parseInt(matcher.group("revision")))
-        .setQualifier(matcher.group("qualifier"))
+        .setQualifier(nullableQualifier != null ? nullableQualifier : "")
         .build();
   }