lib/qx/tool/compiler/Analyser.js
function readDb(cb) {
              fs.exists(t.getDbFilename(), function(exists) {
                if (exists) {
                  fs.readFile(t.getDbFilename(), {encoding: "utf-8"}, cb); 
                } else {
                  cb(null, null); 
                }
              });
            }
function readDb(cb) {
              fs.exists(t.getDbFilename(), function(exists) {
                if (exists) {
                  fs.readFile(t.getDbFilename(), {encoding: "utf-8"}, cb); 
                } else {
                  cb(null, null); 
                }
              });
            }
Reads the db.json, if it exists

@param cb