Use ConvertService to get String representation of input value

This is required to correctly persist values for File[] inputs etc.

Author: imagejan

src/main/java/org/scijava/module/DefaultModuleService.java

@@ -297,9 +297,7 @@ public <T> void save(final ModuleItem<T> item, final T value) {
 			return;
 		}
 
-		// FIXME: Convert to string, instead of just calling toString.
-		// Otherwise many things (e.g. File[]) are persisted improperly.
-		final String sValue = value == null ? "" : value.toString();
+		final String sValue = value == null ? "" : convertService.convert(value, String.class);
 
 		// do not persist if object cannot be converted back from a string
 		if (!convertService.supports(sValue, item.getType())) return;