Calculating only values that are not null in field using ArcGIS Pro

Question

I'm using ArcGIS Pro, the field calculator. I want to populate a hydrant layer with hydrant inspection data. I have two fields from a joined table: field 1 and field 2. I want to populate field 1 with the values from field 2, but only if the values ARE NOT Null. Basically I want to preserve the values in field 1 if the corresponding value in field 2 is Null. I've been trying slight variations of the python code below. But it just populates field 1 with all of field 2 whether there are nulls or not.

I'm a beginner when it comes to Python.

Codeblock:

def reclass(f1,f2):
        if f2 is not None:
            return f2
        else:
            pass

Expression:

reclass(!field1!,!field2!)

Answer 1

I figured it out!

Expression:

Reclass(!field1!,!field2!)

Codeblock:

 def Reclass(f1,f2):
        if f2 is None:
            return f1
        else: 
            return f2

Answer 2

A modified version of Katie's answer if you want to add text to non-null fields

def Reclass(RMNM):
        if RMNM is None:
            return RMNM
        else: 
            return ("RM of " + RMNM)