Backport null defaults support to humble

Signed-off-by: Ryan Friedman <ryan.friedman@avinc.com>

rosidl_generator_cpp/resource/idl__builder.hpp.em

@@ -29,6 +29,7 @@ include_directives = set()
 
 #include <algorithm>
 #include <utility>
+#include <limits>
 
 #include "@(include_base)__struct.hpp"
 #include "rosidl_runtime_cpp/message_initialization.hpp"

rosidl_generator_cpp/resource/idl__struct.hpp.em

@@ -32,6 +32,7 @@ include_directives = set()
 #include <memory>
 #include <string>
 #include <vector>
+// foobar
 
 #include "rosidl_runtime_cpp/bounded_vector.hpp"
 #include "rosidl_runtime_cpp/message_initialization.hpp"

rosidl_generator_cpp/resource/msg__struct.hpp.em

@@ -80,6 +80,9 @@ for member in message.structure.members:
 @[end if]@
 @#>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
 
+#include <math.h>
+#include <limits>
+
 @{
 deprecated_macro_name = \
     '__'.join(['DEPRECATED', package_name] + list(interface_path.parents[0].parts) + [message.structure.namespaced_type.name])
@@ -295,6 +298,12 @@ val = primitive_value_to_cpp(constant.type, constant.value)
 @[   else]@
     @(constant.value)@
 @[   end if];
+@[   elif constant.type.typename == 'float' or constant.type.typename == 'double']@
+@{
+from rosidl_generator_cpp import primitive_value_to_cpp
+val = primitive_value_to_cpp(constant.type, constant.value)
+}@
+    @(val);
 @[  else]@
     @(constant.value);
 @[  end if]@