Checking core structure...
compile_project:10: no matches found: *.in
rm -f calc-core.jar `find . -name \*.class`
(cd src; javac -encoding UTF-8 `find . -name \*.java`)
./calc/Visitor.java:11: error: cannot find symbol
   public boolean visitNullContent(NullContent a);
                                   ^
  symbol:   class NullContent
  location: interface Visitor
./calc/SearchForFuncNameVisitor.java:69: error: cannot find symbol
   public boolean visitNullContent(NullContent a) {
                                   ^
  symbol:   class NullContent
  location: class SearchForFuncNameVisitor
./calc/SearchForValueVisitor.java:57: error: cannot find symbol
   public boolean visitNullContent(NullContent a) {
                                   ^
  symbol:   class NullContent
  location: class SearchForValueVisitor
./calc/Cell.java:57: error: cannot find symbol
         _content = new NullContent(this);
                        ^
  symbol:   class NullContent
  location: class Cell
./calc/Cell.java:160: error: cannot find symbol
            if (_content instanceof NullContent) {
                                    ^
  symbol:   class NullContent
  location: class Cell
./calc/SearchForFuncNameVisitor.java:15: error: cannot find symbol
      if (c instanceof Numeric || c instanceof Referencial || c instanceof NullContent) {
                                                                           ^
  symbol:   class NullContent
  location: class SearchForFuncNameVisitor
6 errors
make: *** [all] Error 1