code: public Map<StatementGroup, Set<Statement>> mapStatements() {
          List<StatementGroup> groups = getStatementGroups();
          final int size = groups.size();
          Map<StatementGroup, Set<Statement>> ret = sizedHashMap(size);
  
          for (final StatementGroup group : groups) {
              List<Statement> stmts = group.getStatements();
              Set<Statement> stmtset;
  
              // No statements? Map to an empty set
              if (stmts == null) {
                  stmtset = emptySet();
                  ret.put(group, stmtset);
                  continue;
              }
  
              stmtset = sizedHashSet(stmts.size());
              stmtset.addAll(stmts);
              ret.put(group, stmtset);
          }
  
          return ret;
      }
docs: Returns a map of {@link StatementGroup statement group} to a {@link Set
  set} of {@link Statement statements}.
  <p>
  The returned map is not backed by the document. If the document is
  modified in any way, the returned map may no longer reflect a correct
  mapping of statement group to statement set.
  </p>
  
  @return {@link Map} of {@link StatementGroup} to {@link Set} of
  {@link Statement Statements}