Fix empty ballots

README.md

@@ -142,7 +142,7 @@ ResultInterface result = mj.deliberate(tally);
 
 Install [maven](https://maven.apache.org), and run:
 
-    mvn test
+    mvn test -DtrimStackTrace=false
 
 > Maven is available as a debian package: `apt install maven`
 

build.gradle

@@ -10,9 +10,11 @@ apply plugin: 'java-library'
 
 // In this section we declare where to find the dependencies of our project
 repositories {
-    // Use jcenter for resolving our dependencies.
     // We can declare any Maven/Ivy/file repository here.
+
+    // Use jcenter for resolving our dependencies.
     //jcenter()
+
     mavenCentral()
 }
 

gradle/wrapper/gradle-wrapper.properties

@@ -1,4 +1,4 @@
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.3-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.4.1-bin.zip
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStorePath=wrapper/dists

src/main/java/fr/mieuxvoter/mj/MajorityJudgmentDeliberator.java

@@ -335,6 +335,10 @@ private Double adjustMeritToAffine(
             BigInteger amountOfJudges,
             int amountOfGrades
     ) {
+        if (maxMerit.compareTo(BigInteger.ZERO) == 0) {
+            return 0.0;
+        }
+
         double meritNormalized = (new BigDecimal(merit).divide(
                 new BigDecimal(maxMerit), 15, RoundingMode.HALF_EVEN
         )).doubleValue();

src/test/java/fr/mieuxvoter/mj/MajorityJudgmentDeliberatorTest.java

@@ -628,6 +628,22 @@ public void execute() throws Throwable {
         assertTrue(caught, "An exception is raised");
     }
 
+    @Test
+    @DisplayName("Allow no ballots")
+    void testNoBallots() {
+        Integer amountOfJudges = 0;
+        DeliberatorInterface mj = new MajorityJudgmentDeliberator();
+        TallyInterface tally =
+                new Tally(
+                        new ProposalTallyInterface[]{
+                                new ProposalTally(new Integer[]{0, 0, 0}),
+                                new ProposalTally(new Integer[]{0, 0, 0}),
+                        },
+                        amountOfJudges
+                );
+        mj.deliberate(tally);
+    }
+
     // …
 
     /**