primitive type variables not nullable ?

[Venkat Akkineni via Digitalmars-d-learn]

	colors = [
		"black" : "నలుపు",
		"white"	: "తెలుపు",
		"red"	: "యెరుపు",
		"green"	: "పచ్చ",
		"blue"	: "నీలం"
	];
	
	writefln("Before: ");
	writeln(colors);
	colors = null;
	writefln("after: ");
	writeln(colors);

This above bit of code is trying to delete all elements at once 
by assigning a null to colors associative array. Interesting 
thing is the write output after assigning null to colors variable 
shows "[]".


Here is the output.

Before:
["blue":"నీలం", "red":"యెరుపు", "white":"తెలుపు", "green":"పచ్చ", 
"black":"నలుపు"]
after:
[]


So primitive types can never be null ? An null assignment would 
set the primitive type variable to a default value ?