snippet throws programming errors

[Cynthia Karl]

The following snippet:

\version "2.19.15"

music = \relative c'' { e2 g, }
 
\score  {
  \new Staff << \key c \major  \music >>
  \layout {
    \context { \Voice \consists "Ambitus_engraver" } 
  }
}

throws the following two programming errors:

        *       programming error: Note-column without heads and stem
                continuing, cross fingers
        *       programming error: note-column has no direction
                continuing, cross fingers

The pdf output looks perfect, so I guess the finger crossing worked.  

These two errors can be eliminated in any one of several ways:

        * eliminate "\key c \major" from the \new Staff statement (!!!)
        * replace "<<...>>" with {...} on the \new Staff statement.
        * eliminate the \context statement in the \layout block

Where can I find out what's happening here?  and is there a way to suppress 
these errors similar to the way that warnings can be suppressed.