[CALCITE-5812] Gradle tasks fails when creating the javadoc aggregation

Exclude "bom" project from the javadoc aggregation since it does not
have "main" and "test" objects causing "tasks" to fail.

Close #222

.github/workflows/main.yml

@@ -58,7 +58,7 @@ jobs:
           fetch-depth: 50
       - name: 'Test'
         run: |
-          ./gradlew --no-parallel --no-daemon build javadoc -Pcheckstyle.version=9.3
+          ./gradlew --no-parallel --no-daemon tasks build javadoc -Pcheckstyle.version=9.3
 
   linux-jdk8-avatica:
     name: 'Linux (JDK 8), Avatica main'
@@ -117,7 +117,7 @@ jobs:
           fetch-depth: 50
       - name: 'Test'
         run: |
-          ./gradlew --no-parallel --no-daemon -Pguava.version=${GUAVA:-14.0.1} build
+          ./gradlew --no-parallel --no-daemon -Pguava.version=${GUAVA:-14.0.1} tasks build
 
   linux-jdk11-middle-aged-guava:
     name: 'Linux (JDK 11), Middle-Aged Guava'
@@ -202,4 +202,4 @@ jobs:
         distribution: 'zulu'
     - name: 'Test'
       run: |
-        ./gradlew --no-parallel --no-daemon build javadoc
+        ./gradlew --no-parallel --no-daemon tasks build javadoc

build.gradle.kts

@@ -140,6 +140,7 @@ val javadocAggregate by tasks.registering(Javadoc::class) {
     description = "Generates aggregate javadoc for all the artifacts"
 
     val sourceSets = allprojects
+        .filter { it.name != "bom" }
         .mapNotNull { it.extensions.findByType<SourceSetContainer>() }
         .map { it.named("main") }
 
@@ -154,6 +155,7 @@ val javadocAggregateIncludingTests by tasks.registering(Javadoc::class) {
     description = "Generates aggregate javadoc for all the artifacts, including test code"
 
     val sourceSets = allprojects
+        .filter { it.name != "bom" }
         .mapNotNull { it.extensions.findByType<SourceSetContainer>() }
         .flatMap { listOf(it.named("main"), it.named("test")) }