New J2K: do not print Unit types

nj2k/src/org/jetbrains/kotlin/nj2k/printing/JKCodeBuilder.kt

@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.nj2k.tree.*
 import org.jetbrains.kotlin.nj2k.tree.visitors.JKVisitorWithCommentsPrinting
 import org.jetbrains.kotlin.nj2k.types.JKContextType
 import org.jetbrains.kotlin.nj2k.types.isInterface
+import org.jetbrains.kotlin.nj2k.types.isUnit
 import org.jetbrains.kotlin.nj2k.types.updateNullability
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
@@ -346,8 +347,10 @@ internal class JKCodeBuilder(context: NewJ2kConverterContext) {
                 it.accept(this)
             }
             renderTokenElement(method.rightParen)
-            printer.print(": ")
+            if (!method.returnType.type.isUnit()) {
-            method.returnType.accept(this)
+                printer.print(": ")
+                method.returnType.accept(this)
+            }
             renderExtraTypeParametersUpperBounds(method.typeParameterList)
             method.block.accept(this)
         }

nj2k/src/org/jetbrains/kotlin/nj2k/types/typesUtils.kt

@@ -184,6 +184,9 @@ fun JKType.isArrayType() =
         else -> false
     }
 
+fun JKType.isUnit() =
+    safeAs<JKClassType>()?.classReference?.fqName == KotlinBuiltIns.FQ_NAMES.unit.asString()
+
 val JKType.isCollectionType: Boolean
     get() = safeAs<JKClassType>()?.classReference?.fqName in collectionFqNames