Collections ManifestTest::toJSON fails on Xcode 7

[ 90%] Building CXX object kv_engine/engines/ep/CMakeFiles/ep-engine_ep_unit_tests.dir/tests/module_tests/collections/vbucket_manifest_entry_test.cc.o

/Users/jenkins/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/tests/module_tests/collections/manifest_test.cc:209:24: error: no viable conversion from 'CollectionEntry::Entry' to 'std::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >')

                     {{CollectionEntry::defaultC},

                       ^~~~~~~~~~~~~~~~~~~~~~~~~

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1326:5: note: candidate constructor not viable: no known conversion from 'CollectionEntry::Entry' to 'const std::__1::basic_string<char> &' for 1st argument

    basic_string(const basic_string& __str);

    ^

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1330:5: note: candidate constructor not viable: no known conversion from 'CollectionEntry::Entry' to 'std::__1::basic_string<char> &&' for 1st argument

    basic_string(basic_string&& __str)

    ^

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1335:31: note: candidate constructor not viable: no known conversion from 'CollectionEntry::Entry' to 'const value_type *' (aka 'const char *') for 1st argument

    _LIBCPP_INLINE_VISIBILITY basic_string(const value_type* __s);

                              ^

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1356:5: note: candidate constructor not viable: no known conversion from 'CollectionEntry::Entry' to 'initializer_list<value_type>' for 1st argument

    basic_string(initializer_list<value_type> __il);

    ^

/Users/jenkins/jenkins/workspace/couchbase-server-unix/kv_engine/engines/ep/tests/module_tests/collections/test_manifest.h:64:5: note: candidate function

    operator CollectionID() const {

    ^