OpenArgument: make all services optional

And do not handle the argument if any are missing.

This pattern reduces the likelihood of plugin initialization
errors when the context does not contain all needed services.

Author: ctrueden

src/main/java/org/scijava/io/console/OpenArgument.java

@@ -51,13 +51,13 @@
 @Plugin(type = ConsoleArgument.class)
 public class OpenArgument extends AbstractConsoleArgument {
 
-	@Parameter
+	@Parameter(required = false)
 	private IOService ioService;
 
-	@Parameter
+	@Parameter(required = false)
 	private DisplayService displayService;
 
-	@Parameter
+	@Parameter(required = false)
 	private LogService log;
 
 	// -- Constructor --
@@ -80,7 +80,14 @@ public void handle(final LinkedList<String> args) {
 			displayService.createDisplay(o);
 		}
 		catch (IOException exc) {
-			log.error(exc);
+			if (log != null) log.error(exc);
 		}
 	}
+
+	// -- Typed methods --
+
+	@Override
+	public boolean supports(final LinkedList<String> args) {
+		return ioService != null && displayService != null && super.supports(args);
+	}
 }