core/rpc: fix for null entries in log filters. Closes #725

You can now specify `null` as a way of saying "not interested in this
topic, match all". core.Filter assumes the zero'd address to be the
wildcard. JSON rpc assumes empty strings to be wildcards.

core/filter.go

@@ -134,7 +134,8 @@ Logs:
 		for i, topics := range self.topics {
 			for _, topic := range topics {
 				var match bool
-				if log.Topics[i] == topic {
+				// common.Hash{} is a match all (wildcard)
+				if (topic == common.Hash{}) || log.Topics[i] == topic {
 					match = true
 				}
 				if !match {

rpc/args.go

@@ -739,10 +739,14 @@ func (args *BlockFilterArgs) UnmarshalJSON(b []byte) (err error) {
 					for j, jv := range argarray {
 						if v, ok := jv.(string); ok {
 							topicdbl[i][j] = v
+						} else if jv == nil {
+							topicdbl[i][j] = ""
 						} else {
 							return NewInvalidTypeError(fmt.Sprintf("topic[%d][%d]", i, j), "is not a string")
 						}
 					}
+				} else if iv == nil {
+					topicdbl[i] = []string{""}
 				} else {
 					return NewInvalidTypeError(fmt.Sprintf("topic[%d]", i), "not a string or array")
 				}