Commit d32f116 was breaking editing.  Add null check.
Commit d32f116 was breaking editing.  Add null check.

See comment in this commit.  It looks like semantically
null and false are the same thing for the tree's readonly
field.

OpenTreeMap/otm-android,OpenTreeMap/otm-android,OpenTreeMap/otm-android,maurizi/otm-android,maurizi/otm-android,maurizi/otm-android