Add error hint for MethodErrors on LogDensityModel #320

Job	Run time
test (1.6, ubuntu-latest, x86, 1)	7m 5s
test (1.6, ubuntu-latest, x64, 1)	5m 4s
test (1.6, macOS-latest, x64, 1)	6m 6s
test (1.6, windows-latest, x64, 1)	11m 46s
test (1, ubuntu-latest, x86, 1)	31m 38s
test (1, ubuntu-latest, x86, 2)	31m 44s
test (1, ubuntu-latest, x64, 1)	5m 23s
test (1, ubuntu-latest, x64, 2)	4m 42s
test (1, macOS-latest, x64, 1)	5m 53s
test (1, macOS-latest, x64, 2)	5m 38s
test (1, windows-latest, x64, 1)	5m 36s
test (1, windows-latest, x64, 2)	5m 33s
test (nightly, ubuntu-latest, x86, 1)	6m 49s
test (nightly, ubuntu-latest, x86, 2)	6m 21s
test (nightly, ubuntu-latest, x64, 1)	4m 55s
test (nightly, ubuntu-latest, x64, 2)	5m 3s
test (nightly, macOS-latest, x64, 1)	5m 39s
test (nightly, macOS-latest, x64, 2)	5m 45s
test (nightly, windows-latest, x64, 1)	6m 52s
test (nightly, windows-latest, x64, 2)	6m 23s
	2h 53m 55s

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