public Map<T, DependencyNode> getNodeMap() {
		return nodeMap;
	}
Class for managing the visiting (processing)  of a set of values where some values depend
on other values being process before them.  In other words, an acyclic directed graph will
be formed where the vertexes are the values and the edges represent dependencies.  Values can
only be removed if they have no dependencies.  Since the graph is acyclic, as values are removed
that have no dependencies, other nodes that depend on those nodes will become eligible for 
processing and removal.  If cycles are introduced, they will eventually cause an IllegalState
exception to occur when removing and processing values.  There is also a hasCycles() method
that can be called before processing to find cycle problems up front without wasting time 
processing values. 

@param <T> the type of value.  Some concrete classes might have restrictions on T.

@see DependencyGraph
@see DeterministicDependencyGraph
Ghidra/Framework/Generic/src/main/java/ghidra/util/graph/AbstractDependencyGraph.java