Fix nil handling in item_type method and add parameter specs

lib/ruby_llm/mcp/parameter.rb

@@ -15,7 +15,7 @@ def initialize(name, type: "string", desc: nil, required: true, default: nil, un
       end
 
       def item_type
-        @items["type"].to_sym
+        @items&.[]("type")&.to_sym
       end
     end
   end

spec/ruby_llm/mcp/parameter_spec.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+RSpec.describe RubyLLM::MCP::Parameter do
+  describe "#item_type" do
+    context "when @items is nil" do
+      it "returns nil" do
+        parameter = described_class.new("test_param", type: "string")
+        expect(parameter.item_type).to be_nil
+      end
+    end
+
+    context "when @items is empty hash" do
+      it "returns nil" do
+        parameter = described_class.new("test_param", type: "string")
+        parameter.items = {}
+        expect(parameter.item_type).to be_nil
+      end
+    end
+
+    context "when @items['type'] is nil" do
+      it "returns nil" do
+        parameter = described_class.new("test_param", type: "string")
+        parameter.items = { "other_key" => "value" }
+        expect(parameter.item_type).to be_nil
+      end
+    end
+
+    context "when @items['type'] has a value" do
+      it "returns the type as a symbol" do
+        parameter = described_class.new("test_param", type: "array")
+        parameter.items = { "type" => "string" }
+        expect(parameter.item_type).to eq(:string)
+      end
+    end
+  end
+
+  describe "#initialize" do
+    it "creates a parameter with default values" do
+      parameter = described_class.new("test_param")
+      expect(parameter.name).to eq("test_param")
+      expect(parameter.type).to eq(:string)
+      expect(parameter.required).to be(true)
+      expect(parameter.items).to be_nil
+    end
+
+    it "creates a parameter with custom values" do
+      parameter = described_class.new("test_param", type: "array", desc: "Test description", required: false)
+      expect(parameter.name).to eq("test_param")
+      expect(parameter.type).to eq(:array)
+      expect(parameter.desc).to eq("Test description")
+      expect(parameter.required).to be(false)
+    end
+  end
+end