View Compilation Error

0_0_10978255_21390.cpp: In member function `void Node::relax()':
0_0_10978255_21390.cpp:31: error: `null' undeclared (first use this function)
0_0_10978255_21390.cpp:31: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_10978255_21390.cpp: At global scope:
0_0_10978255_21390.cpp:43: error: `Node*null' used prior to declaration