private boolean graphDataMissing() {
		FGData data = controller.getFunctionGraphData();
		if (!data.hasResults()) {
			return true;
		}

		FunctionGraph functionGraph = data.getFunctionGraph();
		FGVertex rootVertex = functionGraph.getRootVertex();
		if (rootVertex == null) {
			return true; // this can happen in bad state with undo/redo...not sure how
		}

		AddressSetView addresses = rootVertex.getAddresses();
		FunctionManager functionManager = currentProgram.getFunctionManager();
		Function currentFunctionInMemory = functionManager.getFunctionAt(addresses.getMinAddress());
		return currentFunctionInMemory == null;
	}
Returns true when something destructive has happened to the data upon which the graph has
created, like a memory block move.
Ghidra/Features/FunctionGraph/src/main/java/ghidra/app/plugin/core/functiongraph/FGProvider.java