Make services optional for array/string converters

Especially the ParseService, because otherwise, if you include the
ConvertService in your context without the ParseService, you'll see
warnings that the StringToArrayConverter plugin cannot be instantiated.

Author: ctrueden

src/main/java/org/scijava/convert/ArrayToStringConverter.java

@@ -50,7 +50,8 @@
 @Plugin(type = Converter.class, priority = Priority.VERY_LOW)
 public class ArrayToStringConverter extends AbstractConverter<Object, String> {
 
-	@Parameter private ConvertService convertService;
+	@Parameter(required = false)
+	private ConvertService convertService;
 
 	@Override public boolean canConvert(final Class<?> src, final Class<?> dest) {
 		if (src == null) return false;
@@ -60,6 +61,7 @@ public class ArrayToStringConverter extends AbstractConverter<Object, String> {
 	}
 
 	@Override public boolean canConvert(final Object src, final Class<?> dest) {
+		if (convertService == null) return false;
 		if (!canConvert(src.getClass(), dest)) return false;
 		if (Array.getLength(src) == 0) return true;
 		return convertService.supports(Array.get(src, 0), dest);

src/main/java/org/scijava/convert/StringToArrayConverter.java

@@ -52,10 +52,10 @@
 @Plugin(type = Converter.class, priority = Priority.VERY_LOW)
 public class StringToArrayConverter extends AbstractConverter<String, Object> {
 
-	@Parameter
+	@Parameter(required = false)
 	private ConvertService convertService;
 
-	@Parameter
+	@Parameter(required = false)
 	private ParseService parseService;
 
 	private final ExpressionParser parser = new ExpressionParser();
@@ -75,6 +75,7 @@ public boolean canConvert(final Object src, final Type dest) {
 
 	@Override
 	public boolean canConvert(final Object src, final Class<?> dest) {
+		if (convertService == null || parseService == null) return false;
 
 		// First, ensure the base types conform
 		if (!canConvert(src.getClass(), dest)) return false;