[rf2] report error when any of the specified RF2 sources is a directory

Author: cmark

src/main/java/com/b2international/rf2/RF2Create.java

@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.stream.Collectors;
 
+import com.b2international.rf2.model.RF2Directory;
 import com.b2international.rf2.model.RF2File;
 import com.b2international.rf2.spec.RF2ReleaseSpecification;
 import com.b2international.rf2.spec.RF2Specification;
@@ -99,6 +100,18 @@ public void doRun() throws Exception {
 			sources = Collections.emptyList();
 		}
 
+		boolean validSources = true;
+		for (RF2File source : sources) {
+			if (source instanceof RF2Directory) {
+				console.log("Only .txt and .zip files are accepted as RF2 source files. '%s' is a directory.", source.getPath());
+				validSources = false;
+			}
+		}
+		
+		if (!validSources) {
+			return;
+		}
+		
 		specification
 			.prepare(outputDirectory)
 			.create(new RF2CreateContext(specification, sources, console));