Fix sample body import separator

Author: IgnatBeresnev

dokka-subprojects/plugin-base/src/main/kotlin/org/jetbrains/dokka/base/transformers/pages/DefaultSamplesTransformer.kt

@@ -58,8 +58,38 @@ internal class DefaultSamplesTransformer(val context: DokkaContext) : PageTransf
         return dfs(fqLink, node)
     }
 
+    /**
+     * If both [imports] and [body] are present, it should return
+     *
+     * ```kotlin
+     * import com.example.One
+     * import com.example.Two
+     *
+     * fun main() {
+     *    //sampleStart
+     *    println("Sample function body")
+     *    println("Another line")
+     *    //sampleEnd
+     * }
+     * ```
+     *
+     * If [imports] are empty, it should return:
+     *
+     * ```kotlin
+     * fun main() {
+     *    //sampleStart
+     *    println("Sample function body")
+     *    println("Another line")
+     *    //sampleEnd
+     * }
+     * ```
+     *
+     * Notice the presence/absence of the new line before the body.
+     */
     private fun createSampleBody(imports: List<String>, body: String) =
-        """ |${imports.takeIf { it.isNotEmpty() }?.joinToString { "import $it\n" } ?: ""}
+        // takeIf {} is needed so that joinToString's postfix is not added for empty lists,
+        // and trimMargin() then removes the first empty line
+        """ |${imports.takeIf { it.isNotEmpty() }?.joinToString(separator = "\n", postfix = "\n") { "import $it" } ?: "" }
             |fun main() { 
             |   //sampleStart 
             |   $body 

dokka-subprojects/plugin-base/src/test/kotlin/linkableContent/LinkableContentTest.kt

@@ -213,6 +213,8 @@ class LinkableContentTest : BaseAbstractTest() {
                     assertEquals(
                         """
                         |import p2.${name}Class
+                        |import kotlin.collections.List
+                        |import kotlin.collections.Map
                             |
                             |fun main() { 
                             |   //sampleStart 

dokka-subprojects/plugin-base/src/test/resources/linkable/samples/jsMain/resources/Samples.kt

@@ -5,6 +5,8 @@
 package samples
 
 import p2.JsClass
+import kotlin.collections.List
+import kotlin.collections.Map
 
 class SamplesJs {
 

dokka-subprojects/plugin-base/src/test/resources/linkable/samples/jvmMain/resources/Samples.kt

@@ -5,6 +5,8 @@
 package samples
 
 import p2.JvmClass
+import kotlin.collections.List
+import kotlin.collections.Map
 
 class SamplesJvm {