Add more details as to why a user would want to use nullIf (#806)

There has been some confusion as to the use case of nullIf, this adds a
bit more reasoning in the docs as to how a user might use it!

---------

Co-authored-by: Jens Pryce-Åklundh <[email protected]>

modules/ROOT/pages/functions/scalar.adoc

@@ -692,6 +692,7 @@ The length of the path `p` is returned.
 == nullIf()
 
 The function `nullIf()` returns null if the two given parameters are equivalent, otherwise returns the value of the first parameter.
+This function is the opposite of the xref:functions/scalar.adoc#functions-coalesce[coalesce()] function, which returns a default value if the given value is null.
 
 *Syntax:*
 
@@ -768,6 +769,35 @@ The first parameter, "abc", is returned, as the two parameters are not equivalen
 
 ======
 
+.+nullIf()+
+======
+
+The `nullIf()` function can be used in conjunction with the `coalesce()` function for transforming one data value into another value:
+
+.Query
+[source, cypher, indent=0]
+----
+MATCH (a)
+RETURN a.name AS name, coalesce(nullIf(a.eyes, "brown"), "hazel") AS eyeColor
+----
+
+
+.Result
+[role="queryresult",options="header,footer",cols="2*<m"]
+|===
+
+| +name+      | +eyeColor+
+| +"Alice"+   | +"hazel"+
+| +"Bob"+     | +"blue"+
+| +"Charlie"+ | +"green"+
+| +"Daniel"+  | +"hazel"+
+| +"Eskil"+   | +"blue"+
+2+d|Rows: 5
+
+|===
+
+======
+
 
 [[functions-properties]]
 == properties()