public static IfNotExistsFunction<M> if_not_exists(String path,
            Map<String, ?> defaultValue) {
        return if_not_exists(new PathOperand(path), new LiteralOperand(
                defaultValue));
    }
public static IfNotExistsFunction < M > if_not_exists ( String path , Map < String , ? > defaultValue ) { return if_not_exists ( new PathOperand ( path ) , new LiteralOperand ( defaultValue ) ) ; }
Returns an <code>IfNotExists</code> object which represents an <a href=
"http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.Modifying.html"
>if_not_exists(path, operand)</a> function call; used for building
expression.

<pre>
"if_not_exists (path, operand) – If the item does not contain an attribute
at the specified path, then if_not_exists evaluates to operand; otherwise,
it evaluates to path. You can use this function to avoid overwriting an
attribute already present in the item."
</pre>

@param path
document path to an attribute
@param defaultValue
default value if the attribute doesn't exist

@return an <code>IfNotExists</code> object for map (M) attribute.