Update introduction.md

Author: armanh3k

concepts/nullability/introduction.md

@@ -2,11 +2,11 @@
 
 In Java, the `null` literal is used to denote the absence of a value.
 
-Primitive data types in java all have a default value and therefore can never be `null`.
+Primitive data types in Java all have a default value and therefore can never be `null`.
 By convention, they start with a lowercase letter e.g `int`.
 
-Reference types contain the memory address of an object can have a value of null.
-These variables usually start with an uppercase e.g `String`.
+Reference types contain the memory address of an object and can have a value of `null`.
+They generally start with an uppercase letter, e.g. `String`.
 
 Attempting to assign a primitive variable a value of `null` will result in a compile time error as the variable always holds a primitive value of the type assigned.