private Map . Entry < Variable , ImmutableTerm > applyNullNormalization ( Map . Entry < Variable , ImmutableTerm > substitutionEntry ) { ImmutableTerm value = substitutionEntry . getValue ( ) ; if ( value instanceof ImmutableFunctionalTerm ) { ImmutableTerm newValue = normalizeFunctionalTerm ( ( ImmutableFunctionalTerm ) value ) ; return newValue . equals ( value ) ? substitutionEntry : new AbstractMap . SimpleEntry <> ( substitutionEntry . getKey ( ) , newValue ) ; } return substitutionEntry ; }
Most functional terms do not accept NULL as arguments . If this happens they become NULL .