Added bespoke error for null cases

[jonomacd]

Description: This adds a bespoke null error to the typed Get functions

Benchmark before change:

BenchmarkJsonParserLarge
BenchmarkJsonParserLarge-4                    	  101186	     59316 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserMedium
BenchmarkJsonParserMedium-4                   	  664688	      9127 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserDeleteMedium
BenchmarkJsonParserDeleteMedium-4             	  584113	     16541 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserEachKeyManualMedium
BenchmarkJsonParserEachKeyManualMedium-4      	  697446	      7584 ns/op	     112 B/op	       2 allocs/op
BenchmarkJsonParserEachKeyStructMedium
BenchmarkJsonParserEachKeyStructMedium-4      	  718255	      9049 ns/op	     544 B/op	      12 allocs/op
BenchmarkJsonParserObjectEachStructMedium
BenchmarkJsonParserObjectEachStructMedium-4   	  598053	     14774 ns/op	     496 B/op	      11 allocs/op
BenchmarkJsonParserSmall
BenchmarkJsonParserSmall-4                    	 5438990	      1097 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserEachKeyManualSmall
BenchmarkJsonParserEachKeyManualSmall-4       	 8123079	       726.3 ns/op	      80 B/op	       2 allocs/op
BenchmarkJsonParserEachKeyStructSmall
BenchmarkJsonParserEachKeyStructSmall-4       	 5914904	      1101 ns/op	     184 B/op	       7 allocs/op
BenchmarkJsonParserObjectEachStructSmall
BenchmarkJsonParserObjectEachStructSmall-4    	 3735968	      1712 ns/op	     168 B/op	       6 allocs/op
BenchmarkJsonParserSetSmall
BenchmarkJsonParserSetSmall-4                 	 2382969	      3151 ns/op	     768 B/op	       4 allocs/op
BenchmarkJsonParserDelSmall
BenchmarkJsonParserDelSmall-4                 	 1917996	      4370 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	benchmarks	104.655s

Benchmark after change:

BenchmarkJsonParserLarge
BenchmarkJsonParserLarge-4                    	   98062	     63203 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserMedium
BenchmarkJsonParserMedium-4                   	  570456	      9970 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserDeleteMedium
BenchmarkJsonParserDeleteMedium-4             	  603286	     13375 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserEachKeyManualMedium
BenchmarkJsonParserEachKeyManualMedium-4      	  780256	      9199 ns/op	     112 B/op	       2 allocs/op
BenchmarkJsonParserEachKeyStructMedium
BenchmarkJsonParserEachKeyStructMedium-4      	  419198	     15755 ns/op	     544 B/op	      12 allocs/op
BenchmarkJsonParserObjectEachStructMedium
BenchmarkJsonParserObjectEachStructMedium-4   	  362432	     16357 ns/op	     496 B/op	      11 allocs/op
BenchmarkJsonParserSmall
BenchmarkJsonParserSmall-4                    	 3645873	      1711 ns/op	       0 B/op	       0 allocs/op
BenchmarkJsonParserEachKeyManualSmall
BenchmarkJsonParserEachKeyManualSmall-4       	 5796182	      1012 ns/op	      80 B/op	       2 allocs/op
BenchmarkJsonParserEachKeyStructSmall
BenchmarkJsonParserEachKeyStructSmall-4       	 5057808	      1171 ns/op	     184 B/op	       7 allocs/op
BenchmarkJsonParserObjectEachStructSmall
BenchmarkJsonParserObjectEachStructSmall-4    	 5825636	      1145 ns/op	     168 B/op	       6 allocs/op
BenchmarkJsonParserSetSmall
BenchmarkJsonParserSetSmall-4                 	 3933043	      2098 ns/op	     768 B/op	       4 allocs/op
BenchmarkJsonParserDelSmall
BenchmarkJsonParserDelSmall-4                 	 2888763	      1989 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	benchmarks	93.459s

[buger]

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