bindings: Don't throw a TypeError when 'null' is passed to nullable callback function

third_party/WebKit/Source/bindings/templates/callback_function.cpp.tmpl

 {% from 'utilities.cpp.tmpl' import v8_value_to_local_cpp_value %}
 {% filter format_blink_cpp_source_code %}
 
 {% include 'copyright_block.txt' %}
 
 #include "{{cpp_class}}.h"
 
 {% for filename in cpp_includes %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace blink {
 
+// static
+{{cpp_class}}* {{cpp_class}}::create(ScriptState* scriptState, v8::Local<v8::Value> callback){
+  if (isUndefinedOrNull(callback))
+    return nullptr;
+  return new {{cpp_class}}(scriptState, v8::Local<v8::Function>::Cast(callback));
+}
+
 {{cpp_class}}::{{cpp_class}}(ScriptState* scriptState, v8::Local<v8::Function> callback)
     : m_scriptState(scriptState),
     m_callback(scriptState->isolate(), this, callback) {
   DCHECK(!m_callback.isEmpty());
 }
 
 DEFINE_TRACE({{cpp_class}}) {}
 
 DEFINE_TRACE_WRAPPERS({{cpp_class}}) {
   visitor->traceWrappers(m_callback.cast<v8::Value>());
@@ skipping 39 matching lines @@
     returnValue = cppValue;
     {% endif %}
     return true;
   }
   return false;
 }
 
 }  // namespace blink
 
 {% endfilter %}{# format_blink_cpp_source_code #}