Chat endpoint doesnt actually require message: param

Author: andreibondarev

lib/cohere/client.rb

@@ -14,7 +14,7 @@ def initialize(api_key:, timeout: nil)
     end
 
     def chat(
-      message:,
+      message: nil,
       model: nil,
       stream: false,
       preamble: nil,
@@ -37,7 +37,9 @@ def chat(
       &block
     )
       response = connection.post("chat") do |req|
-        req.body = {message: message}
+        req.body = {}
+
+        req.body[:message] = message if message
         req.body[:model] = model if model
         if stream || block
           req.body[:stream] = true