fix more accidental deletions from the rebase

Author: stevengj

base/docs/helpdb/Base.jl

@@ -1305,6 +1305,13 @@ Compute the inverse error function of a real `x`, defined by ``\\operatorname{er
 """
 erfinv
 
+"""
+    seek(s, pos)
+
+Seek a stream to the given position.
+"""
+seek
+
 """
     besselj0(x)
 
@@ -2588,6 +2595,13 @@ Test whether a floating point number is subnormal.
 """
 issubnormal
 
+"""
+    NullException()
+
+An attempted access to a [`Nullable`](:obj:`Nullable`) with no defined value.
+"""
+NullException
+
 """
     cfunction(function::Function, ReturnType::Type, (ArgumentTypes...))