private boolean isUndefined(Address a) {

		int length = (a.getAddressSpace().getSize()) / 4;
		for (int i = 0; i < length; i++) {
			if (listing.getUndefinedDataAt(a) == null) {
				return false;
			}
			try {
				a = a.addNoWrap(1);
			}
			catch (AddressOverflowException e) {
				return false;
			}
		}
		return true;
	}
Given an address in memory, see if the byte at the named address and the
three consecutive bytes form an address.  If any of the bytes is part
of an instruction or defined data, then we terminate the check.  We are
Interested in cleared bytes.
@param a address that we need to see how represent it textually.
@param string textual representation for the byte.
Ghidra/Features/ByteViewer/src/main/java/ghidra/app/plugin/core/format/AddressFormatModel.java