fix: improve error handling

src/index.ts

@@ -262,7 +262,7 @@ async function main() {
   // Check source path arg.
   if (!sourcePath) {
     indicator.fail('No input file or folder specified.');
-    return;
+    return Promise.reject('No input file or folder specified.');
   }
 
   // Check source exists, is a dir or a file ?
@@ -274,12 +274,11 @@ async function main() {
   // Try to define type of target (file or dir).
   // Assume the target is the same as the source
   let targetIsFile = sourceIsFile;
-  const outputExists = existsSync(outputPath);
 
   // Dir to file is not possible
   if (!sourceIsFile && targetIsFile) {
     indicator.fail('The source is a directory, so the target must be directory, too.');
-    return;
+    return Promise.reject('The source is a directory, so the target must be directory, too.');
   }
 
   // Get source and target parser.
@@ -288,7 +287,7 @@ async function main() {
   const targetParser = targetFormat && getParserFromFormat(targetFormat) || getParserFromFilename(outputPath);
   if (!sourceParser) {
     indicator.fail('No sourceparser was specified.');
-    return;
+    return Promise.reject('No sourceparser was specified.');
   }
   if (!targetParser) {
     indicator.info('No targetparser was specified. Output will be a GeoStyler object.');