check null result

Author: lizekun

geth.go

@@ -20,3 +20,14 @@ func (c *Client) GasPrice() (price *big.Int, err error) {
 	err = c.call("proxy", "eth_gasPrice", param, price)
 	return
 }
+
+func (c *Client) EstimateGas(from, to string, value, gasPrice *big.Int) (limit uint64, err error) {
+	param := M{
+		"value":    value.Text(16),
+		"to":       to,
+		"form":     from,
+		"gasPrice": gasPrice.Text(16),
+	}
+	err = c.call("proxy", "eth_estimateGas", param, &limit)
+	return
+}