fix: Fix exception on empty VssDefinition asset file

If the VssDefinition annotation is missing but the processor is
executed then the necessary asset file can't be found.

- Removes a redundant `maven-publish` plugin

close #43

Signed-Off-By: Mark Hüsers <mark.huesers@etas.com>

vss-processor/build.gradle.kts

@@ -1,6 +1,5 @@
 plugins {
     kotlin("jvm")
-    `maven-publish`
     publish
 }
 

vss-processor/src/main/kotlin/org/eclipse/kuksa/vssprocessor/VssDefinitionProcessor.kt

@@ -85,7 +85,7 @@ class VssDefinitionProcessor(
             val vssDefinitionPath = vssDefinition.vssDefinitionPath
 
             val definitionFile = loadAssetFile(vssDefinitionPath)
-            if (!definitionFile.exists()) {
+            if (definitionFile == null || !definitionFile.exists()) {
                 logger.error("No VSS definition file was found!")
                 return
             }
@@ -97,13 +97,14 @@ class VssDefinitionProcessor(
         }
 
         // Uses the default file path for generated files (from the code generator) and searches for the given file.
-        private fun loadAssetFile(fileName: String): File {
-            val generationPath = codeGenerator.generatedFile.first().absolutePath
+        private fun loadAssetFile(fileName: String): File? {
+            val generatedFile = codeGenerator.generatedFile.firstOrNull() ?: return null
+            val generationPath = generatedFile.absolutePath
             val buildPath = generationPath.replaceAfter(BUILD_FOLDER_NAME, "")
             val assetsFilePath = "$buildPath/$ASSETS_BUILD_DIRECTORY"
             val assetsFolder = File(assetsFilePath)
 
-            return assetsFolder.walk().first { it.name == fileName }
+            return assetsFolder.walk().firstOrNull { it.name == fileName }
         }
 
         private fun generateModelFiles(vssPathToSpecification: Map<VssPath, VssSpecificationSpecModel>) {