Fix Eth::Abi::DecodingError in call method (#105)

* Fix Eth::Abi::DecodingError in call method

* Fix argument address

lib/eth/client.rb

@@ -241,7 +241,7 @@ def call(contract, function_name, *args, **kwargs)
       func = contract.functions.select { |func| func.name == function_name }[0]
       raise ArgumentError, "function_name does not exist!" if func.nil?
       output = call_raw(contract, func, *args, **kwargs)
-      if output.length == 1
+      if output&.length == 1
         return output[0]
       else
         return output
@@ -422,6 +422,7 @@ def call_raw(contract, func, *args, **kwargs)
       end
       raw_result = eth_call(params)["result"]
       types = func.outputs.map { |i| i.type }
+      return nil if raw_result == "0x"
       Eth::Abi.decode(types, raw_result)
     end
 

spec/eth/client_spec.rb

@@ -106,13 +106,21 @@
     subject(:test_key) { Key.new }
     subject(:contract) { Eth::Contract.from_file(file: "spec/fixtures/contracts/dummy.sol") }
     subject(:test_contract) { Eth::Contract.from_file(file: "spec/fixtures/contracts/simple_registry.sol") }
+    let(:erc20_abi_file) { File.read "spec/fixtures/abi/ERC20.json" }
+    let(:address) { Eth::Address.new("0xd496b23d61f88a8c7758fca7560dcfac7b3b01f9").address }
+    subject(:erc20_abi) { JSON.parse erc20_abi_file }
+    subject(:erc20_contract) { Eth::Contract.from_abi(abi: erc20_abi, name: "ERC20", address: address) }
 
     it "call function name" do
       geth_dev_http.deploy_and_wait(contract)
       result = geth_dev_http.call(contract, "get")
       expect(result).to eq(0)
     end
 
+    it "return nil if raw result is 0x" do
+      expect(geth_dev_http.call(erc20_contract, "balanceOf", address)).to be_nil
+    end
+
     it "called function name not defined" do
       expect { geth_dev_http.call(contract, "ge") }.to raise_error ArgumentError
     end