Why is the two parameter constructor called when single parameter constructor is expected?

I have the following two constructors in my base class:

prote开发者_开发技巧cted ExternalSystemException( params Object[] args ) 
    : this( null, null, args ) {}

protected ExternalSystemException( String propertyKeySuffix, 
    params Object[] args ) : this( propertyKeySuffix, null, args ) {}

My child class has the following constructor:

public InvalidPathToOutputFiles(string invalidPath) 
    : base(invalidPath) {}

My client logic instantiates the child class like so:

throw new ChildClass( "goofy" );

When I step through the logic I unexpectedly end up at the base constructor with the parameters ( String propertyKeySuffix, params Object[] args ). I expected the other base class constructor to be called, namely ( params Object[] args ).

Can someone tell me why this is happening?

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The string overload is the best match to the type you are providing to the constructor. The Params are optional (and Object is ambiguous), so since the second overload has a string type that matches the string type you are passing, the second overload is selected.