application/json GETs can have no request body.

spec/param_parser_spec.cr

@@ -30,6 +30,7 @@ describe "ParamParser" do
     params.should eq({"hasan" => "cemal", "name" => "serdar", "age" => "99"})
   end
 
+  context "when content type is application/json" do
     it "parses request body" do
       route = Route.new "POST", "/" { }
 
@@ -44,6 +45,20 @@ describe "ParamParser" do
       params.should eq({"name": "Serdar"})
     end
 
+    it "handles no request body" do
+      route = Route.new "GET", "/" { }
+
+      request = HTTP::Request.new(
+        "GET",
+        "/",
+        headers: HTTP::Headers{"Content-Type": "application/json"},
+      )
+
+      params = Kemal::ParamParser.new(route, request).parse
+      params.should eq({} of String => AllParamTypes)
+    end
+  end
+
   context "when content type is incorrect" do
     it "does not parse request body" do
       route = Route.new "POST", "/" do |env|

src/kemal/param_parser.cr

@@ -38,7 +38,7 @@ class Kemal::ParamParser
   end
 
   def parse_json
-    return unless @request.headers["Content-Type"]? == APPLICATION_JSON
+    return unless @request.body && @request.headers["Content-Type"]? == APPLICATION_JSON
     body = @request.body as String
     json = JSON.parse(body) as Hash
     json.each do |k, v|