Minor fixes, typo and NULL -> nullptr
Minor fixes, typo and NULL -> nullptr

rTreutlein/atomspace,misgeatgit/atomspace,misgeatgit/atomspace,AmeBel/atomspace,AmeBel/atomspace,rTreutlein/atomspace,misgeatgit/atomspace,rTreutlein/atomspace,rTreutlein/atomspace,misgeatgit/atomspace,AmeBel/atomspace,AmeBel/atomspace,misgeatgit/atomspace,AmeBel/atomspace,rTreutlein/atomspace