Fix SystemCallError.new called with nil message value

Author: andrykonchin

core/exception/system_call_error_spec.rb

@@ -53,6 +53,11 @@ def initialize
     e.should be_an_instance_of(@example_errno_class)
   end
 
+  it "sets an error message corresponding to an appropriate Errno class" do
+    e = SystemCallError.new(@example_errno)
+    e.message.should == 'Invalid argument'
+  end
+
   it "accepts an optional custom message preceding the errno" do
     exc = SystemCallError.new("custom message", @example_errno)
     exc.should be_an_instance_of(@example_errno_class)
@@ -81,6 +86,17 @@ def initialize
     SystemCallError.new('foo', 2.9).should == SystemCallError.new('foo', 2)
   end
 
+  it "treats nil errno as unknown error value" do
+    SystemCallError.new(nil).should be_an_instance_of(SystemCallError)
+  end
+
+  it "treats nil custom message as if it is not passed at all" do
+    exc = SystemCallError.new(nil, @example_errno)
+    exc.should be_an_instance_of(@example_errno_class)
+    exc.errno.should == @example_errno
+    exc.message.should == 'Invalid argument'
+  end
+
   it "converts to Integer if errno is a Complex convertible to Integer" do
     SystemCallError.new('foo', Complex(2.9, 0)).should == SystemCallError.new('foo', 2)
   end